http://arxiv.org/abs/2002.09584
The $\lambda$ = 2.06 $\mu$m absorption band of $^{12}$C$^{16}$O$_2$ is widely used for the remote sensing of atmospheric carbon dioxide, making it relevant to many important top-down measurements of carbon flux. The forward models used in the retrieval algorithms employed in these measurements require increasingly accurate line intensity and line shape data from which absorption cross-sections can be computed. To overcome accuracy limitations of existing line lists, we used frequency-stabilized cavity ring-down spectroscopy to measure 39 transitions in the $^{12}$C$^{16}$O$_2$ absorption band. We estimate the relative combined standard uncertainty for the measured intensities to be $u_r$ = 0.09 %, which is dominated by several type B (systematic) contributions each with $u_r$ = 0.04 %. We predicted the $J$-dependence of the measured intensities using two theoretical models: a one-dimensional quantum mechanical model with Herman-Wallis rotation-vibration corrections, and a line-by-line ab initio model [Zak et al. JQSRT 2016;177:31-42]. For the second approach, we fit only a single factor to rescale the theoretical integrated band intensity to be consistent with the measured intensities. We find that the latter approach yields an equally adequate representation of the fitted $J$-dependent intensity data and provides the most physically general representation of the results. Our recommended value for the integrated band intensity equal to 7.180$\times$10$^{-21}$ cm molecule$^{-1}$ $\pm$ 6$\times$10$^{-24}$ cm molecule$^{-1}$ is based on the rescaled ab initio model and corresponds to a fitted scale factor of 1.0065 $\pm$ 0.0002. Comparisons of literature intensity values to our results reveal systematic deviations ranging from $-$1.1 % to 0.4 %.
H. Fleurbaey, H. Yi, E. Adkins, et. al.
Tue, 25 Feb 20
66/76
Comments: 30 pages, 9 figures, 4 tables