Tag Archives: Atomic Physics

Plasma diagnostic potential of 2p4f in N$^+$ — accurate wavelengths and oscillator strengths [CL]

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http://arxiv.org/abs/1503.04498


Radiative emission lines from nitrogen and its ions are often observed in nebulae spectra, where the N$^{2+}$ abundance can be inferred from lines of the 2p4f configuration. In addition, intensity ratios between lines of the 2p3p — 2p3s and 2p4f — 2p3d transition arrays can serve as temperature diagnostics. To aid abundance determinations and plasma diagnostics, wavelengths and oscillator strengths were calculated with high-precision for electric-dipole (E1) transitions from levels in the 2p4f configuration of N$^{+}$. Electron correlation and relativistic effects, including the Breit interaction, were systematically taken into account within the framework of the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Except for the 2p4f – 2p4d transitions with quite large wavelengths and the two-electron-one-photon 2p4f -2s2p$^3$ transitions, the uncertainties of the present calculations were controlled to within 3% and 5% for wavelengths and oscillator strengths, respectively. We also compared our results with other theoretical and experimental values when available. Discrepancies were found between our calculations and previous calculations due to the neglect of relativistic effects in the latter.

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X. Shen, J. Li, P. Jonsson, et. al.
Tue, 17 Mar 15
50/79

Comments: N/A

Radiative charge transfer in cold and ultracold Sulfur atoms colliding with Protons [CL]

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http://arxiv.org/abs/1502.07239


Radiative decay processes at cold and ultra cold temperatures for Sulfur atoms colliding with protons are investigated. The MOLPRO quantum chemistry suite of codes was used to obtain accurate potential energies and transition dipole moments, as a function of internuclear distance, between low-lying states of the SH$^{+}$ molecular cation. A multi-reference configuration-interaction (MRCI) approximation together with the Davidson correction is used to determine the potential energy curves and transition dipole moments, between the states of interest, where the molecular orbitals (MO’s) are obtained from state-averaged multi configuration-self-consistent field (MCSCF) calculations. The collision problem is solved approximately using an optical potential method to obtain radiative loss, and a fully two-channel quantum approach for radiative charge transfer. Cross sections and rate coefficients are determined for the first time for temperatures ranging from 10 $\mu$ K up to 10,000 K. Results are obtained for all isotopes of Sulfur, colliding with H$^{+}$ and D$^{+}$ ions and comparison is made to a number of other collision systems.

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G. Shen, P. Stancil, J. Wang, et. al.
Thu, 26 Feb 15
6/52

Comments: 16 pages, 9 figures, accepted for publication in J Phys B: At. Mol. Opt. Phys

Accurate determination of the free-free Gaunt factor. II – relativistic Gaunt factors [HEAP]

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http://arxiv.org/abs/1502.06788


When modelling an ionised plasma, all spectral synthesis codes need the thermally averaged free-free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum. Until now no data set exists that would meet these needs completely. We have therefore produced a table of relativistic Gaunt factors over a much wider range of parameter space than has ever been produced before. We present tables of the thermally averaged Gaunt factor covering the range log10(gamma^2) = -6 to 10 and log10(u) = -16 to 13 for all atomic numbers Z = 1 through 36. The data were calculated using the relativistic Bethe-Heitler-Elwert (BHE) approximation and were subsequently merged with accurate non-relativistic results in those parts of the parameter space where the BHE approximation is not valid. These data will be incorporated in the next major release of the spectral synthesis code Cloudy. We also produced tables of the frequency integrated Gaunt factor covering the parameter space log10(gamma^2) = -6 to 10 for all values of Z between 1 and 36. All the data presented in this paper are available online.

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P. Hoof, G. Ferland, R. Williams, et. al.
Wed, 25 Feb 15
15/55

Comments: 8 pages, 8 figures, 2 tables

Atom-interferometry constraints on dark energy [CL]

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http://arxiv.org/abs/1502.03888


If dark energy—which drives the accelerated expansion of the universe—consists of a new light scalar field, it might be detectable as a “fifth force” between normal-matter objects, in potential conflict with precision tests of gravity. There has, however, been much theoretical progress in developing theories with screening mechanisms, which can evade detection by suppressing forces in regions of high density, such as the laboratory. One prominent example is the chameleon field. We reduce the effect of this screening mechanism by probing the chameleon with individual atoms rather than bulk matter. Using a cesium matter-wave interferometer near a spherical mass in an ultra-high vacuum chamber, we constrain a wide class of dynamical dark energy theories. Our experiment excludes a range of chameleon theories that reproduce the observed cosmic acceleration.

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P. Hamilton, M. Jaffe, P. Haslinger, et. al.
Mon, 16 Feb 15
48/55

Comments: N/A

Cubic wavefunction deformation of compressed atoms [CL]

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http://arxiv.org/abs/1502.03781


We hypothesize that in a non-metallic crystalline structure under extreme pressures, atomic wavefunctions deform to adopt a reduced rotational symmetry consistent with minimizing interstitial space in the crystal. We exemplify with a simple numeric variational calculation that yields the energy cost of this deformation for Helium to 25%. Balancing this with the free energy gained by tighter packing we obtain the pressures required to effect such deformation. The consequent modification of the structure suggests a decrease in the resistance to tangential stress, and an associated decrease of the crystal’s shear modulus. The atomic form factor is also modified. We also compare with neutron matter in the interior of compact stars.

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P. Portela and F. Llanes-Estrada
Fri, 13 Feb 15
27/63

Comments: 6 pages, 13 figure files

Unified line profiles for hydrogen perturbed by collisions with protons: satellites and asymmetries [SSA]

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http://arxiv.org/abs/1501.05609


We present new calculations of unified line profiles for hydrogen perturbed by collisions with protons. We report on new calculations of the potential energies and dipole moments which allow the evaluation of profiles for the lines of the Lyman series up to Lyman$\delta$ and the Balmer series up to Balmer10. Unified calculations only existed for the lines Lyman$\alpha$ to Lyman$\gamma$ and Balmer$\alpha$ including the H$_2^+$ quasi-molecule. These data are available as online material accompanying this paper and should be included in atmosphere models, in place of the Stark effect of protons, since the quasi-molecular contributions cause not only satellites, but large asymmetries that are unaccounted for in models that assume Stark broadening of electrons and protons are equal.

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I. Pelisoli, M. Santos and S. Kepler
Fri, 23 Jan 15
26/65

Comments: 13 pages, 25 figures. Accepted for publication in MNRAS

Effective collision strengths for excitation and de-excitation of nebular [O III] optical and infrared lines with kappa distributed electron energies [CL]

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http://arxiv.org/abs/1501.03803


We present effective collision strengths for electron excitation and de-excitation of the ten forbidden transitions between the five lowest energy levels of the astronomically abundant doubly-ionised oxygen ion, O^{2+}. The raw collision strength data were obtained from an R-matrix intermediate coupling calculation using the Breit-Pauli relativistic approximation published previously by the authors. The effective collision strengths were calculated with kappa-distributed electron energies and are tabulated as a function of the electron temperature and kappa.

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P. Storey and T. Sochi
Fri, 16 Jan 15
9/50

Comments: 7 pages, 4 figures, 4 tables

Physics of polarized scattering at multi-level atomic systems [SSA]

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http://arxiv.org/abs/1501.02259


The symmetric peak observed in linear polarization in the core of the solar sodium D$_1$ line at 5896 \AA\ has remained enigmatic since its discovery nearly two decades ago. One reason is that the theory of polarized scattering has not been experimentally tested for multi-level atomic systems in the relevant parameter domains, although the theory is continually being used for the interpretation of astrophysical observations. A laboratory experiment that was set up a decade ago to find out whether the D$_1$ enigma is a problem of solar physics or quantum physics revealed that the D$_1$ system has a rich polarization structure in situations where standard scattering theory predicts zero polarization, even when optical pumping of the $m$ state populations of the hyperfine-split ground state is accounted for. Here we show that the laboratory results can be modeled in great quantitative detail if the theory is extended to include the coherences in both the initial and final states of the scattering process. Radiative couplings between the allowed dipole transitions generate coherences in the initial state. Corresponding coherences in the final state are then demanded by a phase closure selection rule. The experimental results for the well understood D$_2$ line are used to constrain the two free parameters of the experiment, collision rate and optical depth, to suppress the need for free parameters when fitting the D$_1$ results.

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J. Stenflo
Mon, 12 Jan 15
58/63

Comments: N/A

Using Atomic Clocks to Detect Gravitational Waves [IMA]

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http://arxiv.org/abs/1501.00996


Atomic clocks have recently reached a fractional timing precision of $<10^{-18}$. We point out that an array of atomic clocks, distributed along the Earth’s orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz gravitational waves (GWs), such as those emitted by supermassive black hole binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, currently envisioned for the eLISA mission.

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A. Loeb and D. Maoz
Wed, 7 Jan 15
50/67

Comments: 2 pages, 1 figure, submitted to Phys. Rev. D

Photoionization of the $3s^23p^4~ ^3P$ and the $3s^23p^4~^1D,~^1S$ states of sulfur: experiment and theory [EPA]

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http://arxiv.org/abs/1412.8715


Photoionization of neutral atomic sulfur in the ground and metastable states was studied experimentally at a photon energy resolution of 44 meV FWHM. Relative cross section measurements were recorded by using tunable vacuum ultraviolet (VUV) radiation in the energy range 9 — 30 eV obtained from a laser-produced plasma and the atomic species were generated by photolysis of molecular precursors. Photoionization of this atom is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. A wealth of resonance features observed in the experimental spectra are spectroscopically assigned and their energies and quantum defects tabulated. The cross-section measurements are compared with state-of-the-art theoretical cross-section calculations obtained from the Dirac Coulomb R-matrix method. Resonances series in the spectra are identified and compared indicating similar features in both the theoretical and experimental spectra.

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M. Barthel, R. Flesch, E. Ruhl, et. al.
Wed, 31 Dec 14
11/32

Comments: Accepted for publication in Physical Review A, 20 pages, 8 figures, 3 tables

Searching for dark matter and variation of fundamental constants with laser and maser interferometry [CL]

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http://arxiv.org/abs/1412.7801


Laser and maser interferometry have proven to be extremely sensitive techniques in searches for exotic new physics, including searches for the aether, tests of Lorentz symmetry and gravitational wave detection. We propose several new uses of laser and maser interferometry for investigating fundamental physics. Any slight variations in the fundamental constants of Nature, which may be induced by dark matter or some yet-to-be-discovered cosmic field, would characteristically alter the phase of a light beam inside an interferometer, which can be measured extremely precisely. Laser and maser interferometry may be applied to searches for the linear-in-time drift of the fundamental constants, detection of topological defect dark matter through transient-in-time effects and for a relic, coherently oscillating condensate, which consists of scalar dark matter fields, through oscillating effects. Our proposed experiments offer sensitivity to variation of the fundamental constants at the fractional level $\sim 10^{-21}$, based on already existing technology.

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Y. Stadnik and V. Flambaum
Tue, 30 Dec 14
24/83

Comments: 4 pages

State resolved data for radiative association of H and p and for photodissociation of H${}_2^+$ [CL]

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http://arxiv.org/abs/1412.2606


The matrix elements and energies needed to calculate vibrational-rotational state resolved cross sections and rate coefficients for radiative association of H and p and for photodissociation of H${}_2^+$ are presented for applications to simulations of chemistry in the early Universe and to stellar atmospheres.

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J. Babb
Tue, 9 Dec 14
21/64

Comments: 8 pages, 1 figure, ApJS accepted

The Leading Correction to the Thomas-Fermi Model at Finite Temperature [CL]

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http://arxiv.org/abs/1412.2402


The semi-classical approach leading to the Thomas-Fermi (TF) model provides a simple universal thermodynamic description of the electronic cloud surrounding the nucleus in an atom. This model is known to be exact at the limit of $Z\rightarrow\infty$, i.e., infinite nuclear charge, at finite density and temperature. Motivated by the zero-temperature case, we show in the current letter that the correction to TF due to quantum treatment of the strongly bound inner-most electrons, for which the semi-classical approximation breaks, scales as $Z^{-1/3}$, with respect to the TF solution. As such, it is more dominant than the quantum corrections to the kinetic energy, as well as exchange and correlation, which are known to be suppressed by $Z^{-2/3}$. We conjecture that this is the leading correction for this model. In addition, we present a different free energy functional for the TF model, and a successive functional that includes the strongly bound electrons correction. We use this corrected functional to derive a self-consistent potential and the electron density in the atom, and to calculate the corrected energy. At this stage, our model has a built-in validity limit, breaking as the L shell ionizes.

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E. Segev and D. Gazit
Tue, 9 Dec 14
55/64

Comments: 5 pages, 4 figures, 1 table

Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron [SSA]

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http://arxiv.org/abs/1410.4850


We describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. We are unaware of any previous ionization balance calculations that have included EIMI, which is usually assumed to be unimportant. Here, we incorporate EIMI cross-section data into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect and can usually be ignored. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.

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M. Hahn and D. Savin
Tue, 21 Oct 14
4/72

Comments: Submitted to the Astrophysical Journal

On the empirical dipole polarizability of He from spectroscopy of HeH$^{+}$ [CL]

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http://arxiv.org/abs/1410.4895


Using a long-range polarization potential for HeH$^{+}$, we can obtain an empirical value for the Boltzmann constant $k_{B}$ with an order of magnitude greater precision than the previous best experimental value based on the dipole polarizability of $^{4}$He. We find that relativistic and QED effects of order $\alpha_{{\rm FS}}^{3}$ in the fine structure constant are crucial in the quadrupole polarizability in order to fit the dipole polarizbility with this precision using the polarization potential. By calculating finite-mass corrections for $^{3}$He, we also present theoretical values for the dipole and quadrupole polarizabilities of $^{3}$He with 9 and 7 digits of precision respectively.

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N. Dattani and M. Puchalski
Tue, 21 Oct 14
20/72

Comments: We thank Krzystof Pachucki, Z-C. Yan, Stephen Lundeen, Richard Drachman, Anand Bhatia, Robert Le Roy, Grzegorz Lach, and Jim Mitroy for helpful discussions

Cosmological Evolution of Fundamental Constants: From Theory to Experiment [CL]

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http://arxiv.org/abs/1410.2765


In this paper we discuss a possible cosmological time evolution of fundamental constants from the theoretical and experimental point of views. On the theoretical side, we explain that such a cosmological time evolution is actually something very natural which can be described by mechanisms similar to those used to explain cosmic inflation. We then discuss implications for grand unified theories, showing that the unification condition of the gauge coupling could evolve with cosmological time. Measurements of the electron-to-proton mass ratio can test grand unified theories using low energy data. Following the theoretical discussion, we review the current status of precision measurements of fundamental constants and their potential cosmological time dependence.

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X. Calmet and M. Keller
Mon, 13 Oct 14
15/43

Comments: N/A

Energy levels, radiative rates and electron impact excitation rates for transitions in Fe XIV [SSA]

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http://arxiv.org/abs/1409.4214


Energies and lifetimes are reported for the lowest 136 levels of Fe XIV, belonging to the (1s$^2$2s$^2$2p$^6$) 3s$^2$3p, 3s3p$^2$, 3s$^2$3d, 3p$^3$, 3s3p3d, 3p$^2$3d, 3s3d$^2$, 3p3d$^2$ and 3s$^24\ell$ configurations. Additionally, radiative rates, oscillator strengths and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions. Theoretical lifetimes determined from these radiative rates for most levels show satisfactory agreement with earlier calculations, as well as with measurements. Electron impact excitation collision strengths are also calculated with the Dirac atomic $R$-matrix code (DARC) over a wide energy range up to 260 Ryd. Furthermore, resonances have been resolved in a fine energy mesh to determine effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron velocities. Results are listed for all 9180 transitions among the 136 levels over a wide range of electron temperatures, up to 10$^{7.1}$ K. Comparisons are made with available results in the literature, and the accuracy of the present data is assessed.

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K. Aggarwal and F. Keenan
Tue, 16 Sep 14
56/63

Comments: Text including figures and tables: 17 p, figures: 5, tables: 8, will be published in MNRAS (2014)

Energy levels, radiative rates and electron impact excitation rates for transitions in Be-like Cl XIV, K XVI and Ge XXIX [SSA]

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http://arxiv.org/abs/1409.3745


Results for energy levels, radiative rates and electron impact excitation (effective) collision strengths for transitions in Be-like Cl XIV, K XVI and Ge XXIX are reported. For the calculations of energy levels and radiative rates the General-purpose Relativistic Atomic Structure Package ({\sc grasp}) is adopted, while for determining the collision strengths and subsequently the excitation rates, the Dirac Atomic R-matrix Code ({\sc darc}) is used. Oscillator strengths, radiative rates and line strengths are listed for all E1, E2, M1 and M2 transitions among the lowest 98 levels of the $n \le$ 4 configurations. Furthermore, lifetimes are provided for all levels and comparisons made with available theoretical and experimental results. Resonances in the collision strengths are resolved in a fine energy mesh and averaged over a Maxwellian velocity distribution to obtain the effective collision strengths. Results obtained are listed over a wide temperature range up to 10$^{7.8}$ K, depending on the ion.

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K. Aggarwal and F. Keenan
Mon, 15 Sep 14
13/47

Comments: Text: 10p, Figs. 3, Tables 17 Will be published in Physica Scripta 89 (2014) 000000

New Atomic probes for Dark Matter detection: Axions, Axion-like particles and Topological Defects [CL]

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http://arxiv.org/abs/1409.2986


We present a brief overview of recently proposed detection schemes for axion, axion-like pseudoscalar particle and topological defect dark matter. We focus mainly on the possibility of using atomic and molecular systems for dark matter detection. For axions and axion-like particles, these methods are complementary probes to ongoing photon-axion interconversion experiments and astrophysical observations. For topological defects, these methods are complementary to conventional astrophysical search schemes based on gravitational signatures.

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Y. Stadnik and V. Flambaum
Thu, 11 Sep 14
12/67

Comments: Review. 10 pages

Parity-violating interactions of cosmic fields with atoms, molecules, and nuclei: Concepts and calculations for laboratory searches and extracting limits [CL]

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http://arxiv.org/abs/1409.2564


We propose methods and present calculations that can be used to search for evidence of cosmic fields by investigating the parity-violating effects, including parity nonconservation amplitudes and electric dipole moments, that they induce in atoms. The results are used to constrain important fundamental parameters describing the strength of the interaction of various cosmic fields with electrons, protons, and neutrons. Candidates for such fields are dark matter (including axions) and dark energy, as well as several more exotic sources described by standard-model extensions. Existing parity nonconservation experiments in Cs, Dy, Yb, and Tl are combined with our calculations to directly place limits on the interaction strength between the temporal component, b_0, of a static pseudovector cosmic field and the atomic electrons, with the most stringent limit of |b_0^e| < 7*10^(-15) GeV, in the laboratory frame of reference, coming from Dy. From a measurement of the nuclear anapole moment of Cs, and a limit on its value for Tl, we also extract limits on the interaction strength between the temporal component of this cosmic field, as well as a related tensor cosmic-field component d_00, with protons and neutrons. The most stringent limits of |b_0^p| < 4*10^(-8) GeV and |d_00^p| < 5*10^(-8) for protons, and |b_0^n| < 2*10^(-7) GeV and |d_00^n| < 2*10^(-7) for neutrons (in the laboratory frame) come from the results using Cs. Axions may induce oscillating P- and T-violating effects in atoms and molecules through the generation of oscillating nuclear magnetic quadrupole and Schiff moments, which arise from P- and T-odd intranuclear forces and from the electric dipole moments of constituent nucleons. Nuclear-spin-independent parity nonconservation effects may be enhanced in diatomic molecules possessing close pairs of opposite-parity levels in the presence of time-dependent interactions.

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B. Roberts, Y. Stadnik, V. Dzuba, et. al.
Wed, 10 Sep 14
4/66

Comments: 18 pages, 3 figures, 4 tables

Reaction Studies of Neutral Atomic ${\rm C}$ with ${\rm H_3^+}$ using a Merged-Beams Apparatus [IMA]

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http://arxiv.org/abs/1408.4696


We have investigated the chemistry of ${\rm C + H_3^+}$ forming CH$^+$, CH$_2^+$, and CH$_3^+$. These reactions are believed to be some of the key gas-phase astrochemical processes initiating the formation of organic molecules in molecular clouds. For this work we have constructed a novel merged fast-beams apparatus which overlaps a beam of molecular ions onto a beam of ground-term neutral atoms. Here we present cross section data for forming CH$^+$ and CH$_2^+$ at collision energies from $\approx 9$ meV to $\approx20$ and 3 eV, respectively. Using these data we have derived thermal rate coefficients for reaction temperatures from $\approx72$ K to $\approx2.3 \times 10^5$ and $3.4 \times 10^4$ K, respectively. For the formation of CH$_3^+$ we are able only to put an upper limit on the rate coefficient. Our results for CH$^+$ and CH$_2^+$ are in good agreement with the mass-scaled results from a previous ion trap study of ${\rm C + D_3^+}$ at a reaction temperature of $\sim 1000$ K. At molecular cloud temperatures our thermal rate coefficient for forming CH$^+$ lies a factor of $\sim 2-4$ below the Langevin rate coefficient currently given in astrochemical databases and below the published semi-classical calculations. Our results for CH$_2^+$ formation are a factor of $\sim 26$ above the semi-classical results. Astrochemical databases do not currently include this channel.

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A. OConnor, X. Urbain, J. Stutzel, et. al.
Thu, 21 Aug 14
61/61

Comments: N/A

Improved V II log($gf$) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937 [SSA]

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http://arxiv.org/abs/1408.4175


New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Use of two spectrometers, independent radiometric calibration methods, and independent data analysis routines enables a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log {\epsilon}(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

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M. Wood, J. Lawler, E. Hartog, et. al.
Wed, 20 Aug 14
5/73

Comments: 32 pages, 7 tables (3 machine-readable), 8 figures; accepted for publication in ApJS

Limiting P-odd interactions of cosmic fields with electrons, protons and neutrons [CL]

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http://arxiv.org/abs/1404.2723


We propose methods for extracting limits on the strength of P-odd interactions of pseudoscalar and pseudovector cosmic fields with electrons, protons and neutrons. Candidates for such fields are dark matter (including axions) and dark energy, as well as several more exotic sources described by standard-model extensions. Calculations of parity nonconserving amplitudes and atomic electric dipole moments induced by these fields are performed for H, Li, Na, K, Rb, Cs, Ba+, Tl, Dy, Fr, and Ra+. From these calculations and existing measurements in Dy, Cs and Tl, we constrain the interaction strengths of the parity-violating static pseudovector cosmic field to be 7*10^(-15) GeV with an electron, and 3*10^(-8) GeV with a proton.

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B. Roberts, Y. Stadnik, V. Dzuba, et. al.
Tue, 12 Aug 14
7/65

Comments: 6 pages, 1 figure

Improved limits on Standard Model Extension parameters and applications to axion dark matter searches [CL]

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http://arxiv.org/abs/1408.2184


Nuclear many-body effects create new possibilities in tests of the fundamental symmetries of nature and searches for axion dark matter. We calculate the proton and neutron spin contributions for a wide range of nuclei of experimental interest. We reconsider experiments, which search for evidence of CPT- and Lorentz invariance-violating couplings, using a $^{3}$He/$^{129}$Xe comagnetometer and show that the $^{3}$He/$^{129}$Xe system is in fact particularly sensitive to proton interaction parameters. From existing data, we derive a limit on the Standard Model Extension (SME) parameter $|\tilde{b}_{\perp}^p| < 1.6 \times 10^{-33}$ GeV, which improves on the world’s previously most stringent limit by a factor of 35. We also extend previous analysis of nuclear anapole moment data for Cs to obtain new limits on several other SME parameters.

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Y. Stadnik and V. Flambaum
Tue, 12 Aug 14
11/65

Comments: 6 pages

Axion-induced effects in atoms, molecules and nuclei: parity non-conservation, anapole moments, electric dipole moments, and spin-gravity and spin-axion momentum couplings [CL]

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http://arxiv.org/abs/1312.6667


We show that the interaction of an axion field, or in general a pseudoscalar field, with the axial-vector current generated by an electron through a derivative-type coupling can give rise to a time-dependent mixing of opposite-parity states in atomic and molecular systems. Likewise, the analogous interaction of an axion field with the axial-vector current generated by a nucleon can give rise to time-dependent mixing of opposite-parity states in nuclear systems. This mixing can induce oscillating electric dipole moments, oscillating parity non-conservation effects and oscillating anapole moments in such systems. By adjusting the energy separation between the opposite-parity states of interest to match the axion mass energy, axion-induced experimental observables can be enhanced by many orders of magnitude. Oscillating atomic electric dipole moments can also be generated by axions through hadronic mechanisms, namely the P,T-violating nucleon-nucleon interaction and through the axion-induced electric dipole moments of valence nucleons, which comprise the nuclei. The axion field is modified by the Earth’s gravitational field. The interaction of the spin of either an electron or nucleon with this modified axion field leads to axion-induced observable effects. These effects, which are of the form $\mathbf{g} \cdot \mathbf{\sigma}$, differ from the axion-wind effect, which has the form $\mathbf{p}_{\textrm{a}} \cdot \mathbf{\sigma}$.

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Y. Stadnik and V. Flambaum
Tue, 12 Aug 14
34/65

Comments: 14 pages, 1 figure

Emission and recombination coefficients for hydrogen with kappa-distributed electron energies [CL]

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http://arxiv.org/abs/1408.2213


We provide a data set of emission and recombination coefficients of hydrogen using a kappa-distribution of electron energies rather than the more traditional Maxwell-Boltzmann (MB) distribution. The data are mainly relevant to thin and relatively cold plasma found in planetary nebulae and H II regions. The data set extends the previous data sets provided by Storey and Hummer which were computed using a MB distribution. The data set, which is placed in the public domain, is structured as a function of electron number density, temperature and kappa. An interactive fortran data server is also provided as an accessory to probe the data and obtain Lagrange-interpolated values for any choice of all three variables between the explicitly computed values.

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P. Storey and T. Sochi
Tue, 12 Aug 14
49/65

Comments: 3 pages

Accurate determination of the free-free Gaunt factor; I – non-relativistic Gaunt factors [HEAP]

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http://arxiv.org/abs/1407.5048


Modern spectral synthesis codes need the thermally averaged free-free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum emitted by an ionized plasma. Until now no set of data exists that would meet this need in a fully satisfactory way. We have therefore undertaken to produce a table of very accurate non-relativistic Gaunt factors over a much wider range of parameters than has ever been produced before. We first produced a table of non-averaged Gaunt factors, covering the parameter space log10(epsilon_i) = -20 to +10 and log10(w) = -30 to +25. We then continued to produce a table of thermally averaged Gaunt factors covering the parameter space log10(gamma^2) = -6 to +10 and log10(u) = -16 to +13. Finally we produced a table of the frequency integrated Gaunt factor covering the parameter space log10(gamma^2) = -6 to +10. All the data presented in this paper are available online.

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P. Hoof, R. Williams, K. Volk, et. al.
Mon, 21 Jul 14
35/55

Comments: 10 pages, 5 tables, 3 figures

Quantum reactive scattering of O($^3$P)+H$_2$ at collision energies up to 4.4 eV [CL]

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http://arxiv.org/abs/1407.3325


We report the results of quantum scattering calculations for the O($^3$P)+H$_2$ reaction for a range of collision energies from 0.4 to 4.4 eV, important for astrophysical and atmospheric processes. The total and state-to-state reactive cross sections are calculated using a fully quantum time-independent coupled-channel approach on recent potential energy surfaces of $^{3}A’$ and $^{3}A”$ symmetry. A larger basis set than in the previous studies was used to ensure convergence at higher energies. Our results agree well with the published data at lower energies and indicate the breakdown of reduced dimensionality approach at collision energies higher than 1.5 eV. Differential cross sections and momentum transfer cross sections are also reported.

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M. Gacesa and V. Kharchenko
Tue, 15 Jul 14
62/64

Comments: 11 pages, draft; submitted to JCP

Sensitivity coefficients to $α$-variation for astrophysically relevant transitions in Ni II [CL]

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http://arxiv.org/abs/1407.1860


We calculated the dependence of the transition frequencies on the fine-structure constant $\alpha$ ($q$-factors) for Ni~II. Nickel is one of the few elements with high sensitivity to $\alpha$-variation, whose lines are observed at high redshifts. This makes it a sensitive probe for $\alpha$-variation on the cosmological timescale. The electronic structure of Ni II ion was treated within the configuration interaction (CI) method using Dirac-Coulomb Hamiltonian.

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E. Konovalova, M. Kozlov and R. Imanbaeva
Fri, 11 Jul 14
24/49

Comments: N/A

Dissociative recombination measurements of NH$^+$ using an ion storage ring [IMA]

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http://arxiv.org/abs/1407.0538


We have investigated dissociative recombination (DR) of NH$^+$ with electrons using a merged beams configuration at the TSR heavy-ion storage ring located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present our measured absolute merged beams recombination rate coefficient for collision energies from 0 to 12 eV. From these data we have extracted a cross section which we have transformed to a plasma rate coefficient for the collisional plasma temperature range from $T_{\rm pl} = 10$ to $18000$ K. We show that the NH$^+$ DR rate coefficient data in current astrochemical models are underestimated by up to a factor of $\sim 9$. Our new data will result in predicted NH$^+$ abundances lower than calculated by present models. This is in agreement with the sensitivity limits of all observations attempting to detect NH$^+$ in interstellar clouds.

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O. Novotny, M. Berg, D. Bing, et. al.
Thu, 3 Jul 14
26/42

Comments: July 1st 2014: Accepted for publication in ApJ

Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs [SSA]

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http://arxiv.org/abs/1406.4591


Aims: Hydrogen deficient white dwarfs are characterized by very dense, fluid-like atmospheres of complex physics and chemistry that are still poorly understood. The incomplete description of these atmospheres by the models results in serious problems with the description of spectra of these stars and subsequent difficulties in derivation of their surface parameters. Here, we address the problem of infrared (IR) opacities in the atmospheres of cool white dwarfs by direct $ab$ $initio$ simulations of IR absorption of dense helium.
Methods: We applied state-of-the-art density functional theory-based quantum molecular dynamics simulations to obtain the time evolution of the induced dipole moment. The IR absorption coefficients were obtained by the Fourier transform of the dipole moment time autocorrelation function.
Results: We found that a dipole moment is induced due to three- and more-body simultaneous collisions between helium atoms in highly compressed helium. This results in a significant IR absorption that is directly proportional to $\rm \rho_{\rm He}^3$, where $\rho_{\rm He}$ is the density of helium. To our knowledge, this absorption mechanism has never been measured or computed before and is therefore not accounted for in the current atmosphere models. It should dominate the other collisionally induced absorptions (CIA), arising from $\rm H-He$ and $\rm H_2-He$ pair collisions, and therefore shape the IR spectra of helium-dominated and pure helium atmosphere cool white dwarfs for $\rm He/H>10^4$.
Conclusions: Our work shows that there exists an unaccounted IR absorption mechanism arising from the multi-collisions between He atoms in the helium-rich atmospheres of cool white dwarfs, including pure helium atmospheres. This absorption may be responsible for a yet unexplained frequency dependence of near- and mid- IR spectra of helium-rich stars.

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P. Kowalski
Thu, 19 Jun 14
52/62

Comments: 4 pages, 7 figures, accepted for publication in Astronomy & Astrophysics (Letter)

Basics of the NLTE physics [SSA]

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http://arxiv.org/abs/1406.3553


Basic assumptions of the NLTE approximation in stellar atmospheres are summarized. The assumptions of thermodynamic equilibrium, local thermodynamic equilibrium (LTE), and non-LTE (NLTE) are compared. It is emphasized that LTE is a poor approximation if radiative transitions dominate in stellar atmospheres. The equations of kinetic equilibrium and methods of their solution are discussed.

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J. Kubat
Mon, 16 Jun 14
35/54

Comments: in Determination of Atmospheric Parameters of B-, A-, F- and G-Type Stars, E. Niemczura et al. eds., Springer, in press

Hyperfine dependent $gf$-values of Mn I lines in the 1.49 $-$ 1.80 $μ$m H-band [SSA]

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http://arxiv.org/abs/1406.2942


The three Mn I lines at 17325, 17339 and 17349 \AA~are among the 25 strongest lines ($\log(gf)>0.5$) in the H-band. They are all heavily broadened due to hyperfine structure and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infra-red (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines can not be described in the conventional way by the diagonal $A$ and $B$ hyperfine interaction constants. The off-diagonal hyperfine interaction not only has large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and $gf$-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, agreement between our synthetic and experimental spectra was achieved. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modelled in the relevant region, $1.73-1.74$ $\mu$m using our theoretically predicted $gf$-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and $gf$-values for all the $3d^54s({^7S})4d$ e$^{6}$D $-$ $3d^54s({^7S})4f$ w$^{6}$F hyperfine lines are available as supplementary material online, whereas only the stronger lines are presented and discussed in detail in this paper.

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M. Andersson, J. Grumer, N. Ryde, et. al.
Thu, 12 Jun 14
22/50

Comments: 24 pages, 6 figures, 3 tables (more data tables will be available online when published in Astrophysical Journal Supplement Series)

Searches for topological defect dark matter via non-gravitational signatures [CL]

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http://arxiv.org/abs/1405.5337


We propose schemes for the detection of topological defect dark matter using pulsars and other luminous extraterrestrial systems via non-gravitational signatures. The dark matter field, which makes up a defect, may interact with standard model particles, including quarks and the photon, resulting in the alteration of their masses. When a topological defect passes through a pulsar, its mass, radius and internal structure may be altered, resulting in a pulsar `quake’. A topological defect may also function as a cosmic dielectric material with a frequency-dependent index of refraction, which would give rise to the time delay of a periodic extraterrestrial light or radio signal, and the dispersion of a light or radio source in a similar manner to an optical lens. The biggest advantage of such astrophysical observations over recently proposed terrestrial detection methods is the much higher probability of a defect been found in the vast volumes of outer space compared with one passing through Earth itself.

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Y. Stadnik and V. Flambaum
Thu, 22 May 14
3/48

Comments: 5 pages

Hyperfine-changing transitions in $^3$He II and other one-electron ions by electron scattering [CL]

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http://arxiv.org/abs/1405.4893


We consider the spin-exchange (SE) cross section in electron scattering from $^3$He\,{\scriptsize II}, which drives the hyperfine-changing \hbox{3.46 cm} (8.665 GHz) line transition. Both the analytical quantum defect method — applicable at very low energies — and accurate R-matrix techniques for electron-He$^+$ scattering are employed to obtain SE cross sections. The quantum defect theory is also applied to electron collisions with other one-electron ions in order to demonstrate the utility of the method and derive scaling relations. At very low energies, the hyperfine-changing cross sections due to e$-$He$^+$ scattering are much larger in magnitude than for electron collisions with neutral hydrogen, hinting at large rate constants for equilibration. Specifically, we obtain rate coefficients of $K(10\,{\rm K}) = 1.10 \times 10^{-6}\,\rm cm^3/s$ and $K(100\,{\rm K}) = 3.49\times 10^{-7}\,\rm cm^3/s$.

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K. Bartschat and H. Sadeghpour
Wed, 21 May 14
23/45

Comments: 9 pages, 5 figures, Accepted for Astrophysical Journal

Implementation and Application of the Relativistic Equation of Motion Coupled-cluster Method for the Excited States of Closed-shell Atomic Systems [CL]

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http://arxiv.org/abs/1405.1936


We report the implementation of equation-of-motion coupled-cluster (EOMCC) method in the four-component relativistic framework with the spherical atomic potential to generate the excited states from a closed-shell atomic configuration. This theoretical development will be very useful to carry out high precision calculations of varieties of atomic properties in many atomic systems. We employ this method to calculate excitation energies of many low-lying states in a few Ne-like highly charged ions, such as Cr XV, Fe XVII, Co XVIII and Ni XIX ions, and compare them against their corresponding experimental values to demonstrate the accomplishment of the EOMCC implementation. The considered ions are apt to substantiate accurate inclusion of the relativistic effects in the evaluation of the atomic properties and are also interesting for the astrophysical studies. Investigation of the temporal variation of the fine structure constant (\alpha) from the astrophysical observations is one of the modern research problems for which we also estimate the \alpha sensitivity coefficients in the above ions.

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D. Nandy, Y. Singh and B. Sahoo
Fri, 9 May 14
8/54

Comments: 12 pages, 4 figures

Energy levels, radiative rates and electron impact excitation rates for transitions in Si II [IMA]

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http://arxiv.org/abs/1405.0184


Energies for the lowest 56 levels, belonging to the 3s$^2$3p, 3s3p$^2$, 3p$^3$, 3s$^2$3d, 3s3p3d, 3s$^2$4$\ell$ and 3s$^2$5$\ell$ configurations of Si II, are calculated using the {\sc grasp} (General-purpose Relativistic Atomic Structure Package) code. Analogous calculations have also been performed (for up to 175 levels) using the Flexible Atomic Code ({\sc fac}). Furthermore, radiative rates are calculated for all E1, E2, M1 and M2 transitions. Extensive comparisons are made with available theoretical and experimental energy levels, and the accuracy of the present results is assessed to be better than 0.1 Ryd. Similarly, the accuracy for radiative rates (and subsequently lifetimes) is estimated to be better than 20% for most of the (strong) transitions. Electron impact excitation collision strengths are also calculated, with the Dirac Atomic R-matrix Code ({\sc darc}), over a wide energy range up to 13 Ryd. Finally, to determine effective collision strengths, resonances are resolved in a fine energy mesh in the thresholds region. These collision strengths are averaged over a Maxwellian velocity distribution and results listed over a wide range of temperatures, up to 10$^{5.5}$ K. Our data are compared with earlier $R$-matrix calculations and differences noted, up to a factor of two, for several transitions. Although scope remains for improvement, the accuracy for our results of collision strengths and effective collision strengths is assessed to be about 20% for a majority of transitions.

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K. Aggarwal and F. Keenan
Fri, 2 May 14
28/47

Comments: Text: 8 pages, Tables: 6, Figures: 8 Will appear in MNRAS (2014)

K-shell photoionization of Be-like Boron (B$^+$) Ions: Experiment and Theory [HEAP]

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http://arxiv.org/abs/1405.0073


Absolute cross sections for the K-shell photoionization of Be-like boron ions were measured with the ion-photon merged-beams technique at the Advanced Light Source synchrotron radiation facility. High-resolution spectroscopy with E/$\Delta$E up to 8800 ($\Delta$E $\sim$ 22 meV) covered the energy ranges 193.7 — 194.7 eV and 209 — 215 eV. Lifetimes of the strongest resonances are determined with relative uncertainties down to approximately 4% for the broadest resonance. The measured resonance strengths are consistent with 60 % $\rm 1s^22s^2$ $^1S$ ground-state and 40 % $\rm 1s^22s2p$ $^3P^o$ metastable-state ions in the primary ion beam and confirmed by comparison with independent absolute photo-recombination heavy-ion storage-ring measurements with B$^{2+}$ ions using the principle of detailed balance. Experimental determination of the line width for the $\rm 1s2s^22p$ $^1$P$^{\rm o}$ resonance gives a value of 47 $\pm$ 2 meV and compares favourably to a theoretical estimate of 47 meV from the R-matrix with pseudo-states (RMPS) method. The measured line widths of the $\rm 1s2s2p^2$ $^3$P, $^3$D resonances are 10.0 $\pm$ 2 meV and 32 $\pm$ 3meV, respectively, compared to RMPS theoretical estimates of 9 meV and 34 meV.

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A. Mueller, S. Schippers, R. Phaneuf, et. al.
Fri, 2 May 14
35/47

Comments: 23 pages, 6 figures, 2 tables, accepted for publication in J. Phys. B

A Laboratory log(gf) Measurement of the Ti II 15873.84 Å H-band Line in Support of SDSS-III APOGEE [SSA]

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http://arxiv.org/abs/1404.5944


The SDSS-III APOGEE collaboration has identified a single useable line in the H-band spectra of APOGEE target stars arising from a singly ionized species. This line of Ti II (${\lambda}_{air}$ = 15873.84 {\AA}) is therefore of great importance for use in stellar surface gravity, or log(g), determinations via the Saha equation. While a theoretical estimate of the line strength exists, to date no laboratory measurement of the line strength has been reported. Herein we report an absolute laboratory transition probability measurement for this important Ti II line. A relative line strength measurement is made of the Ti II H-band line of interest and a reference line with a previously reported absolute transition probability. This ratio is measured using multiple spectra of a high-current water-cooled HC lamp recorded with a calibrated FT-IR spectrometer.

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M. Wood, J. Lawler and M. Shetrone
Thu, 24 Apr 14
31/64

K-Shell Photoionization of B-like Oxygen (O$^{3+}$) Ions: Experiment and Theory [HEAP]

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http://arxiv.org/abs/1404.5185


Absolute cross sections for the {\it K}-shell photoionization of boron-like (B-like) O$^{3+}$ ions were measured by employing the ion-photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/$\Delta$E $\approx$ 5000 ($\approx$ 110 meV, FWHM) was achieved with photon energy from 540 eV up to 600 eV. Several theoretical approaches, including R-Matrix, Multi-Configuration Dirac-Fock and Screening Constant by Unit Nuclear Charge were used to identify and characterize the strong 1s $\rightarrow$ 2p and the weaker 1s $\rightarrow$ 3p resonances observed in the {\it K}-shell spectra of this ion. The trend of the integrated oscillator strength and autoionisation width (natural line width) of the strong $\rm 1s \rightarrow 2p$ resonances along the first few ions of the B-like sequence is discussed.

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B. McLaughlin, J. Bizau, D. Cubaynes, et. al.
Tue, 22 Apr 14
44/54

Sensitivity of Tunneling-Rotational Transitions in Ethylene Glycol to Variation of Electron-to-Proton Mass Ratio [CL]

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http://arxiv.org/abs/1401.6561


Ethylene glycol in its ground conformation has tunneling transition with the frequency about 7 GHz. This leads to a rather complicated tunneling-rotational spectrum. Because tunneling and rotational energies have different dependence on the electron-to-proton mass ratio $\mu$, this spectrum is highly sensitive to the possible $\mu$ variation. We used simple 14 parameter effective Hamiltonian to calculate dimensionless sensitivity coefficients $Q_\mu$ of the tunneling-rotational transitions and found that they lie in the range from $-17$ to $+18$. Ethylene glycol has been detected in the interstellar medium. All this makes it one of the most sensitive probes of $\mu$ variation at the large space and time scales.

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A. Viatkina and M. Kozlov
Tue, 25 Mar 14
63/79

Spacecraft Clocks and Relativity: Prospects for Future Satellite Missions [EPA]

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http://arxiv.org/abs/1402.6698


The successful miniaturization of extremely accurate atomic clocks invites prospects for satellite missions to perform precise timing experiments. This will allow effects predicted by general relativity to be detected in Earth’s gravitational field. In this paper we introduce a convenient formalism for studying these effects, and compute the fractional timing differences generated by them for the orbit of a satellite capable of accurate time transfer to a terrestrial receiving station on Earth, as proposed by planned missions. We find that (1) Schwarzschild perturbations would be measurable through their effects both on the orbit and on the signal propagation, (2) frame-dragging of the orbit would be readily measurable, and (3) in optimistic scenarios, the spin-squared metric effects may be measurable for the first time ever. Our estimates suggest that a clock with a fractional timing inaccuracy of $10^{-16}$ on a highly eccentric Earth orbit will measure all these effects, while for a low Earth circular orbit like that of the Atomic Clock Ensemble in Space Mission, detection will be more challenging.

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R. Angelil, P. Saha, R. Bondarescu, et. al.
Fri, 28 Feb 14
10/54

Electron-impact excitation of Fe$^{2+}$: a comparison of intermediate coupling frame transformation, Breit-Pauli and Dirac R-matrix calculations [GA]

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http://arxiv.org/abs/1402.4743


Modeling the spectral emission of low-charge iron group ions enables the diagnostic determination of the local physical conditions of many cool plasma environments such as those found in H II regions, planetary nebulae, active galactic nuclei etc. Electron-impact excitation drives the population of the emitting levels and, hence, their emissivities. By carrying-out Breit-Pauli and intermediate coupling frame transformation (ICFT) R-matrix calculations for the electron-impact excitation of Fe$^{2+}$ which both use the exact same atomic structure and the same close-coupling expansion, we demonstrate the validity of the application of the powerful ICFT method to low-charge iron group ions. This is in contradiction to the finding of Bautista et al. [Ap.J.Lett, 718, L189, (2010)] who carried-out ICFT and Dirac R-matrix calculations for the same ion. We discuss possible reasons.

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N. Badnell and C. Ballance
Thu, 20 Feb 14
40/52

Improved Ni I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937 [SSA]

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http://arxiv.org/abs/1402.4457


Atomic transition probability measurements for 371 Ni I lines in the UV through near IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.

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M. Wood, J. Lawler, C. Sneden, et. al.
Wed, 19 Feb 14
29/50

Atom Interferometry in Space: Thermal Management and Magnetic Shielding [CL]

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http://arxiv.org/abs/1402.1707


Atom interferometry is an exciting tool to probe fundamental physics. It is considered especially apt to test the universality of free fall using two different sorts of atoms. The increasing sensitivity required for this kind of experiment sets severe requirements on its environments, instrument control, and systematic effects. This can partially be mitigated by going to space as was proposed, for example, in the STE-QUEST mission. However, the requirements on the instrument are still very challenging. For example, the specifications of STE-QUEST mission imply that the Feshbach coils of the atom interferometer are allowed to change their radius only by about 70 nm or 7x10E-5 % due to thermal expansion although they consume an average power of 22 W. Also Earth’s magnetic field has to be suppressed by a factor $10^5$. We show in this article that with the right design such thermal and magnetic requirements can indeed be met and that these are not an impediment for the exciting physics possible with atom interferometers in space.

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A. Milke, A. Kubelka, N. Gurlebeck, et. al.
Mon, 10 Feb 14
36/49

{\it K}-Shell Photoionization of B-like Atomic Nitrogen Ions: Experiment and Theory [CL]

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http://arxiv.org/abs/1402.0519


Measurements of absolute cross sections for the {\it K}-shell photoionization of B-like atomic nitrogen ions were carried out utilizing the ion-photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/$\Delta$E $\approx$ 13,500 was the maximum resolution achieved. We have investigated two photon energy regions: 404 eV — 409 eV and 439 eV — 442 eV. Resonance peaks found in the experimental measured cross sections are compared with theoretical estimates from the multi-configuration Dirac – Fock, R-matrix and empirical methods, allowing identification of the strong 1s $\rightarrow$ 2p and the weaker 1s $\rightarrow$ 3p resonances in the observed {\it K}-shell spectra of this B-like nitrogen ion.

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Wed, 5 Feb 14
30/61

The Continuum Emission Spectrum of Hf 2-2 near the Balmer Limit and the ORL versus CEL abundance and temperature Discrepancy [SSA]

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http://arxiv.org/abs/1401.5630


The continuum spectrum of the planetary nebula Hf 2-2 close to the Balmer discontinuity is modeled in the context of the long standing problem of the abundance and temperature discrepancy found when analyzing optical recombination lines and collisionally excited forbidden lines in nebulae. Models are constructed using single and double Maxwell-Boltzmann distributions as well as kappa-distributions for the energies of the free electrons. New results for the necessary continuum and line emission coefficients are presented calculated with kappa-distributed energies. The best fit to the observed continuum spectrum is found to be a model comprising two components with dramatically different temperatures and with a Maxwell-Boltzmann distribution of electron energies. On the basis of a chi-squared analysis, this model is strongly favored over a model with kappa-distributed electron energies.

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Thu, 23 Jan 14
4/70

Ipopv2: Photoionization of Ni XIV — a test case [SSA]

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http://arxiv.org/abs/1401.3122


Several years ago, M. Asplund and coauthors (2004) proposed a revision of the Solar composition. The use of this new prescription for Solar abundances in standard stellar models generated a strong disagreement between the predictions and the observations of Solar observables. Many claimed that the Standard Solar Model (SSM) was faulty, and more specifically the opacities used in such models. As a result, activities around the stellar opacities were boosted. New experiments (J. Bailey at Sandia on Z-Pinch, The OPAC consortium at LULI200) to measure directly absorbtion coefficients have been realized or are underway. Several theoretical groups (CEA-OPAS, Los Alamos Nat. Lab., CEA-SCORCG, The Opacity Project – The Iron Project (IPOPv2)) have started new sets of calculations using different approaches and codes. While the new results seem to confirm the good quality of the opacities used in SSM, it remains important to improve and complement the data currently available. We present recent results in the case of the photoionization cross sections for Ni XIV (Ni13+ ) from IPOPv2 and possible implications on stellar modelling.

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Wed, 15 Jan 14
55/67

Collision Strengths for [O III] Optical and Infrared Lines [CL]

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http://arxiv.org/abs/1311.6517


We present electron collision strengths and their thermally averaged values for the forbidden lines of the astronomically abundant doubly-ionized oxygen ion, O^{2+}, in an intermediate coupling scheme using the Breit-Pauli relativistic terms as implemented in an R-matrix atomic scattering code. We use several atomic targets for the R-matrix scattering calculations including one with 72 atomic terms. We also compare with new results obtained using the intermediate coupling frame transformation method. We find spectroscopically significant differences against a recent Breit-Pauli calculation for the excitation of the [O III] lambda 4363 transition but confirm the results of earlier calculations.

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Wed, 27 Nov 13
26/43

Scattering properties of dark atoms and molecules [CL]

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http://arxiv.org/abs/1311.6468


There has been renewed interest in the possibility that dark matter exists in the form of atoms, analogous to those of the visible world. An important input for understanding the cosmological consequences of dark atoms is their self-scattering. Making use of results from atomic physics for the potentials between hydrogen atoms, we compute the low-energy elastic scattering cross sections for dark atoms. We find an intricate dependence upon the ratio of the dark proton to electron mass, allowing for the possibility to “design” low-energy features in the cross section. Dependences upon other parameters, namely the gauge coupling and reduced mass, scale out of the problem by using atomic units. We derive constraints on the parameter space of dark atoms by demanding that their scattering cross section does not exceed bounds from dark matter halo shapes. We discuss the formation of molecular dark hydrogen in the universe, and determine the analogous constraints on the model when the dark matter is predominantly in molecular form.

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Wed, 27 Nov 13
40/43

Laboratory atomic transition data for precise optical quasar absorption spectroscopy [CEA]

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http://arxiv.org/abs/1311.2949


Quasar spectra reveal a rich array of important astrophysical information about galaxies which intersect the quasar line of sight. They also enable tests of the variability of fundamental constants over cosmological time and distance-scales. Key to these endeavours are the laboratory frequencies, isotopic and hyperfine structures of various metal-ion transitions. Here we review and synthesize the existing information about these quantities for 43 transitions which are important for measuring possible changes in the fine-structure constant, alpha, using optical quasar spectra, i.e. those of Na, Mg, Al, Si, Ca, Cr, Mn, Fe, Ni and Zn. We also summarize the information currently missing that precludes more transitions being used. We present an up-to-date set of coefficients, q, which define the sensitivity of these transitions to variations in alpha. New calculations of isotopic structures and q coefficients are performed for SiII and TiII, including SiII 1808 and TiII 1910.6/1910.9 for the first time. Finally, simulated absorption-line spectra are used to illustrate the systematic errors expected if the isotopic/hyperfine structures are omitted from profile fitting analyses.
To ensure transparency, repeatability and currency of the data and calculations, we supply a comprehensive database as Supporting Information. This will be updated as new measurements and calculations are performed.

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Thu, 14 Nov 13
37/49

The STARK-B database as a resource for \textquotedblleft STARK" widths and shifts data: State of advancement and program of development [SSA]

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http://arxiv.org/abs/1311.2846


\textquotedblleft Stark” broadening theories and calculations have been extensively developed for about 50 years and can now be applied to many needs, especially for accurate spectroscopic diagnostics and modeling. This requires the knowledge of numerous collisional line profiles. Nowadays, the access to such data via an online database becomes essential. STARK-B is a collaborative project between the Astronomical Observatory of Belgrade and the Laboratoire d’\’Etude du Rayonnement et de la mati\`ere en Astrophysique (LERMA). It is a database of calculated widths and shifts of isolated lines of atoms and ions due to electron and ion collisions (impacts). It is devoted to modeling and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas, laser equipments and technological plasmas. Hence, the domain of temperatures and densities covered by the tables is wide and depends on the ionization degree of the considered ion. STARK-B has been fully opened since September 2008 and is in free access.
The first stage of development was ended in autumn 2012, since all the existing data calculated with the impact semiclassical-perturbation method and code by Sahal-Br\’echot, Dimitrijevi\’c and coworkers have now been implemented. We are now beginning the second stage of the development of STARK-B. The state of advancement of the database and our program of development are presented here, together with its context within VAMDC. VAMDC (Virtual Atomic and Molecular Data Center) is an international consortium which has built a secure, documented, flexible interoperable platform e-science permitting an automated exchange of atomic and molecular data.

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Wed, 13 Nov 13
6/56

Stark broadening data for spectral lines of rare-earth elements: Nb III [SSA]

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http://arxiv.org/abs/1311.1948


The electron-impact widths for 15 doubly charged Nb ion lines have been theoretically determined by using the modified semiempirical method. Using the obtained results, we considered the influence of the electron-impact mechanism on line shapes in spectra of chemically peculiar stars and white dwarfs.

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Mon, 11 Nov 13
30/39

Anomalies in radiation-collisional kinetics of Rydberg atoms induced by the effects of dynamical chaos and the double Stark resonance [SSA]

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http://arxiv.org/abs/1311.1499


Radiative and collisional constants of excited atoms contain the matrix elements of the dipole transitions and when they are blocked one can expect occurring a number of interesting phenomena in radiation-collisional kinetics. In recent astrophysical studies of IR emission spectra it was revealed a gap in the radiation emitted by Rydberg atoms ($RA$) with values of the principal quantum number of $n\approx10$. Under the presence of external electric fields a rearrangement of $RA$ emission spectra is possible to associate with manifestations of the Stark effect. The threshold for electric field ionization of $RA$ is $E\approx3\cdot10^{4}$ V/cm for states with $n>10$. This means that the emission of $RA$ with $n\ge10$ is effectively blocked for such fields. In the region of lower electric field intensities the double Stark resonance (or F\”{o}rster resonance) becomes a key player. On this basis it is established the fact that the static magnetic or electric fields may strongly affect the radiative constants of optical transitions in the vicinity of the F\”{o}ster resonance resulting, for instance, in an order of magnitude reduction of the intensity in some lines. Then, it is shown in this work that in the atmospheres of celestial objects lifetimes of comparatively long-lived $RA$ states and intensities of corresponding radiative transitions can be associated with the effects of dynamic chaos via collisional ionization. The F\”{o}ster resonance allows us to manipulate the random walk of the Rydberg electron ($RE$) in the manifold of quantum levels and hence change the excitation energies of $RA$, which lead to anomalies in the IR spectra.

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Fri, 8 Nov 13
46/58

Stark widths of Ar III spectral lines in the atmospheres of subdwarf B stars [SSA]

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http://arxiv.org/abs/1311.1346


Using semiclassical perturbation approach in impact approximation, we have calculated Stark widths for 32 spectral lines of doubly charged argon (Ar III). Oscillator strengths are calculated using Hartree-Fock method with relativistic correction (HFR) and an atomic model including 17 configurations. Energy levels are taken from NIST database. For perturbing levels for which the corresponding energy does not exist in NIST database, the calculated energies are used. Our widths are compared with the experimental results. The results presented here are of interest for modelling and investigation of stellar atmospheres since argon in different ionization stages is observed in many astrophysical objects. Finally, the importance of Stark broadening mechanism is studied in the atmospheric conditions of sdB stars. Electron impact Stark widths are compared to thermal Doppler widths as a function of temperature and optical depth of atmospheric layers.

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Thu, 7 Nov 13
20/60

Hunting for topological dark matter with atomic clocks [CL]

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http://arxiv.org/abs/1311.1244


The cosmological applications of atomic clocks so far have been limited to searches of the uniform-in-time drift of fundamental constants. In this paper, we point out that a transient in time change of fundamental constants can be induced by dark matter objects that have large spatial extent, and are built from light non-Standard Model fields. The stability of this type of dark matter can be dictated by the topological reasons. We point out that correlated networks of atomic clocks, some of them already in existence, can be used as a powerful tool to search for the topological defect dark matter, thus providing another important fundamental physics application to the ever-improving accuracy of atomic clocks. During the encounter with a topological defect, as it sweeps through the network, initially synchronized clocks will become desynchronized. Time discrepancies between spatially-separated clocks are expected to exhibit a distinct signature, encoding defect’s space structure and its interaction strength with the Standard Model fields.

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Thu, 7 Nov 13
32/60

Stark broadening of B IV lines for astrophysical and laboratory plasma research [SSA]

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http://arxiv.org/abs/1311.1330


Stark broadening parameters for 36 multiplets of B IV have been calculated using the semi-classical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series and temperature dependence.

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Thu, 7 Nov 13
54/60

The OIV 1407.3Å/1401.1Å emission-line ratio in a plasma [SSA]

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http://arxiv.org/abs/1311.1054


Line ratio of O IV 1407.3 \AA/1401.1 \AA\- is calculated using mostly our own atomic and collisional data. Energy levels and oscillator strengths needed for this calculation have been calculated using a Hartree-Fock relativistic (HFR) approach. The electron collision strengths introduced in the statistic equilibrium equations are fitted by Line ratio of O IV 1407.3 \AA/1401.1 \AA\- is calculated using mostly our own atomic and collisional data. Energy levels and oscillator strengths needed for this calculation have been calculated using a Hartree-Fock relativistic (HFR) approach. The electron collision strengths introduced in the statistic equilibrium equations are fitted by polynomials for different energies. Comparison has also been made with available theoretical results. The provided line ratio has been obtained for a set of electron densities from $10^{8}$ cm$^{-3}$ to $10^{13}$ cm$^{-3}$ and for a fixed temperature of 50 000 K.

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Wed, 6 Nov 13
23/56

Energy levels and radiative rates for transitions in Ti VII [SSA]

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http://arxiv.org/abs/1311.0650


We report calculations of energy levels, radiative rates, oscillator strengths and line strengths for transitions among the lowest 231 levels of Ti VII. The general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 231 levels, although calculations have been performed for a much larger number of levels (159,162). In addition, lifetimes for all 231 levels are listed. Comparisons are made with existing results and the accuracy of the data is assessed. In particular, the most recent calculations reported by Singh {\em et al} [Can J. Phys. {\bf 90} (2012) 833] are found to be unreliable, with discrepancies for energy levels of up to 1 Ryd and for radiative rates of up to five orders of magnitude for several transitions, particularly the weaker ones. Based on several comparisons among a variety of calculations with two independent codes, as well as with the earlier results, our listed energy levels are estimated to be accurate to better than $1\%$ (within 0.1 Ryd), whereas results for radiative rates and other related parameters should be accurate to better than $20\%$.

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Tue, 5 Nov 13
38/73

A Comprehensive X-ray Absorption Model for Atomic Oxygen

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An analytical formula is developed to represent accurately the photoabsorption cross section of O I for all energies of interest in X-ray spectral modeling. In the vicinity of the Kedge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer- and inner-shell direct photoionization, including significant shake-up and shake-off processes that result in photoionization-excitation and double photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from XSTAR and SPEX spectral models.

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Date added: Tue, 8 Oct 13