Low Temperature Broadening Coefficients in the n2 Band of Chloromethane

The methyl chloride has, in the later years, taken a special place in atmospheric studies. Following the decrease of CFC-gazes production, it became
one of the main source of chlorine ions in our atmosphere. As such it plays a
major role in the ozone depletion. Its origin is multiple: biomass burnings,
tropical forests and human industry. An extensive study of methyl chloride
is mandatory to be able to monitor ozone depletion and atmospheric activity.
In this work, we studied the N2-broadening coefficients in the QR(J,3)
sub-branch of the n2 band of chloromethane. We focused ourselves on low
temperatures, from 200 K to room temperature. The spectra were recorded
with a high resolution tunable diode laser spectrometer. For each line, at
each temperature, we measured the collisional half-width with four different
nitrogen pressures, ranging from 12 to 35 mbar.
We retrieved the collisional N2-broadening coeffiients by fitting on the experimental lineshape the Voigt profile and the Rautian and Galatry models,
which take into account the Dicke narrowing effect. We then analyzed the
temperature and the J dependences of the collisional broadening coefficient.
Finally, we compared our results with previous studies.