Line intensities and self-broadening coefficients of methyl chloride in the 10 µm region

Abstract

We performed the first systematic measurements of line intensities and pressure broadening coefficients of ro-vibrational absorption transitions of the ν6 perpendicular band of CH335Cl and CH337Cl isotopologues. The spectra were recorded in the spectral region between 920 and 1130 cm−1 with a high-resolution Fourier transform spectrometer. A multi-pressure fitting technique was used to fit a series of seven spectra at pressures of CH3Cl ranging from 1.02 to 10.24 mbar to derive these parameters for about 2132 transitions with 1 ≤ J ≤ 55 and 0 ≤ K ≤ 12. The line intensities were discussed as a function of the rotational quantum numbers, and were used to derive the transition dipole moments squared for each line. The analysis of these moments allows us to derive a consistent set of line intensity parameters such as vibrational transition moments, band intensity as well as Herman-Wallis coefficients. The results were found to be in satisfactory agreement with databases and with low resolution measurements of band intensity.The rotational dependencies of the self-broadening coefficients have been clearly observed and modeled using an empirical polynomial law. The average accuracies have been estimated to be around 4 and 5% for line intensities and self-broadening coefficients respectively.