Room temperature oxygen- and air-broadening coefficients for the ν6 band of methyl iodide
Methyl iodide is the chief iodine-containing atmospheric constituent and, as it is naturally produced in the oceans, is believed to play a role in the formation of marine clouds, that influence the terrestrial radiative budget by scattering the incoming radiation [1]. Since sounding from satellites is an efficient way to study the global distribution of a trace gas, the bands that fall into the atmospheric transparency windows, e.g., the ν6 band of methyl iodide, and their spectroscopic characteristics are of particular interest for atmospheric applications.
The goal of the present work is to provide theoretical estimates of line-broadening coefficients of CH3I-O2 and CH3I-air in a wide range of rotational quantum numbers (0 ≤ J ≤ 70 and K ≤ 20) typically required by databases [2-3]. For these purposes a semi-classical (Robert-Bonamy approach with classically calculated “exact” trajectories) [4] and a semi-empirical (analytical expression of the Anderson theory fitted on some experimental values via an empirical correction factor) [5] methods are utilized. The comparison of these results with a set of experimental data [6] for the case of CH3I-O2 and with two sets of experimental data [6, 7] for CH3I-air proves that both methods provide good estimates of line-broadening.
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[3] N. Jacquinet-Husson, et al., Journal of Molecular Spectroscopy 2016, 327, 31–72.
[4] J. Buldyreva, et al., Physical Chemistry Chemical Physics 2011, 13, 20326–20334.
[5] A.D. Bykov, et al., Molecular Physics 2004, 102, 1653-1658.
[6] Y. Attafi, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 2019, 239, 106679.
[7] E. Raddaoui, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 2020, 246, 106934.