N2 and O2 pressure broadening and pressure shift in the 4ν2 band of 16O12C32S

To measure accurately OCS concentrations in planetary atmospheres, it is important to know precisely nitrogen and oxygen pressure broadening and pressure-induced shift coefficients for the lines used in the retrievals. We present in this study the corresponding coefficients for lines of the P and R branches of the 4ν2 band of the primary isotopologue of carbonyl sulfide (16O12C32S).For this purpose, infrared absorption spectra of a natural carbonyl sulfide (OCS) gas sample were recorded at an unapodized resolution of 0.004 cm−1, at room temperature for different pressures of N2 and O2, using a Bruker IFS125HR spectrometer at the LISA Laboratory in France. The line parameters were derived using the multispectrum fitting method applied to the measured shapes of the lines, including the interference effects caused by the line overlaps.The results are compared with earlier measurements and with values calculated using a semi-classical model based upon the Robert and Bonamy formalism that reproduces rather well the experimental m (m=−J for P(J) lines and m=J+1 for R(J) lines) quantum number dependence of the N2 and O2 broadening coefficients. On the other hand most of the lines studied here have positive shift coefficients, which do not show any systematic dependence on m. However, in previous studies of the ν3, 2ν3 and ν2 bands, these coefficients were negative for all lines.

► With Fourier transform spectrometer, infrared absorption spectra of OCS gas sample were recorded. ► We have measured N2 and O2 pressure broadening and pressure induced shift coefficients. ► We have calculated these coefficients using a semi-classical model (Robert and Bonamy formalism). ► Using the measured and theoretical results, we have deduced those related to an air perturber.