N2-Broadening Study in the n2 Band of methyl chloride

Since the diminution of utilization of the CFC gases following the Montreal Protocol [1], methyl chloride has become one of the main sources of chlorine ions in the atmosphere [2], as the main sources are not only anthropomorphic activities, but also tropical forests [2] and biomass burnings [3]. In order to monitor with enough reliability the importance of methyl chloride in our atmosphere, one needs to determine his spectral parameters with high precision.

In the present work, we have measured N2-broadening coefficients in the ν2 band of methyl chloride between 1335 and 1370 cm-1. The measurements were performed with a high resolution tunable diode laser spectrometer [4], for 15 lines in the P and R branches, with J ranging from 4 to 20 and K varying from 2 to 7. For each line, four measurements of the collisional half-width were realized, with different nitrogen pressure, from around 15 to 55 mbar.

Collisional broadening coefficients were retrieved from the fit of Voigt [5], Rautian [6] and Galatry [7] line profiles on the experimental data. For the last two line-shapes, the Dicke narrowing effect [8] was taken into account. We analyzed the angular dependence and compared our results with previous studies in the ν1 [9] and ν3 [10] bands.

References

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