A complete listing of sulfur dioxide self-broadening coefficients for atmospheric applications by coupling infrared and microwave spectroscopy to semiclassical calculations

Abstract Sulfur dioxide (SO 2 ) is a molecule of proved atmospheric relevance, the main sources being anthropogenic, which is one of the main causes of acid rains. Besides, it is also of interest in astrophysics, as it is present in the atmosphere of Venus and in star forming regions. For these reasons SO 2 is one of the target molecules in all of the most important spectroscopic databases which collect the spectroscopic line-by-line parameters for atmospheric remote sensing, astrophysics soundings, and climate changing investigations. Although over the years the spectroscopic properties of this molecule have been widely studied, and line-by-line listings of line positions and intensities have been compiled, at present an analogous systematic and complete database of broadening coefficients is still lacking. The aim of this work is to fill in this vacancy, starting from self-broadening coefficients, by coupling experimental measurements to theoretical calculations. The laboratory experiments are carried out for 12 pure rotational transitions of the vibrational ground state (and 2 of vibrational excited states) and for 25 ro-vibrational lines of the ν 1 band, lying in the 9 µm atmospheric window. Theoretical calculations of broadening coefficients are performed employing a semiclassical formalism based on the ATC (Anderson–Tsao–Curnutte) approximation. From the interplay between theory and experiment the vibrational and quantum number dependence of the collisional cross-sections is first assessed and studied and then a complete database of self-broadening coefficients for 1635 transitions in a wide quantum number range ( 0 ≤ K ″ a ≤ 16 , 2 ≤ J ″ ≤ 68 ) is compiled, presented and made available.