N2-Broadening for Methyl Chloride at Low Temperature by Diode-Laser Spectroscopy

Using a tunable diode-laser spectrometer, we have measured N2-broadening coefficients of 87 individual rovibrational lines in the P and R branches of the ν3 band of methyl chloride (CH335Cl) at 203.2 K. These lines with J values ranging from 2 to 22 and K from 0 to 6 are located in the range 711–751 cm−1. Most of the collisional widths are obtained by modeling the spectral region from the superposition of overlapping Voigt or Rautian profiles. We have reviewed and completed previous measurements of N2-broadening coefficients at room temperature in the ν3 band, in order to compare them to the low-temperature data. A semiclassical calculation, including electrostatic, induction, and dispersion energy contributions, has provided results that are in reasonable agreement with the experimental data at room temperature, but generally larger than the data at low temperature for small or medium J values. The temperature dependence of the collisional broadenings derived from a simple power law has been determined both experimentally and theoretically.