http://arxiv.org/abs/1802.07566
R-matrix calculations combined with the adiabatic-nuclei-rotation and Coulomb-Born approximations are used to compute electron-impact rotational rate coefficients for two open-shell diatomic cations of astrophysical interest: the hydoxyl and sulphanyl ions, OH$^+$ and SH$^+$. Hyperfine resolved rate coefficients are deduced using the infinite-order-sudden approximation. The propensity rule $\Delta F=\Delta j=\Delta N=\pm 1$ is observed, as is expected for cations with a large dipole moment. A model for OH$^+$ excitation in the Orion Bar photon-dominated region (PDR) is presented which nicely reproduces Herschel observations for an electron fraction $x_e=10^{-4}$ and an OH$^+$ column density of $3\times 10^{13}$~cm$^{-2}$. Electron impact electronic excitation cross sections and rate coefficients for the ions are also presented.
J. Hamilton, A. Faure and J. Tennyson
Thu, 22 Feb 18
20/60
Comments: 8 pages, 5 figures, 6 tables, accepted for publication in MNRAS