Line broadening, shifting and mixing parameters for the ν1 + ν3 band of OCS perturbed by N2 and O2

Abstract

In this paper, we report measured Rosenkranz N2- and O2-broadening, induced pressure-shift and mixing coefficients for OCS in the ν1 + ν3 band, using a multi-pressure fitting technique applied to the measured shapes of the lines, including the interference effects caused by the line overlaps. These measurements were made by analysing six laboratory absorption spectra recorded at 0.004 cm−1 resolution using the Fourier transform spectrometer Bruker IFS125HR located at the Laboratoire Interuniversitaire des Systèmes Atmosphériques, in Créteil. The spectra have been recorded in the 1850–3000 cm−1 wave number range at 295 K, using a multipass absorption cell with an optical path of 3.249 m. The total sample pressures ranged from 5.97 to 83.28 Torr with OCS volume mixing ratios between 0.001 and 0.013 in nitrogen or oxygen. We have been able to determine the N2- and O2-pressure-broadening coefficients of 81 ν1 + ν3 transitions with rotational quantum number J up to 50. The measured N2- and O2-broadening coefficients range from 0.0815 ± 0.0698 to 0.1169 ± 0.1027 cm−1 atm−1 at 295 K, respectively. Most of the measured pressure shifts are positive. The reported N2- and O2-induced pressure-shift coefficients vary from about −0.0103 ± 0.0092 to 0.0097 ± 0.0092 cm−1 atm−1, respectively. We have examined the dependence of the measured broadening parameters on the quantum number m (m = −J for the P branch and m = J + 1 for the R branch) and also developed an empirical expression to describe the broadening coefficients in terms of |m|. On average, this empirical expression reproduces the measured broadening coefficients to within 2%. Using a semi-classical Robert and Bonamy formalism, the theoretical broadening coefficients have been calculated at room temperature and compared with the experimental results. The theoretical results of the broadening coefficients are in very good overall agreement with the experimental data (2%).