Diode-laser measurements and calculations of H 2-broadening coefficients in the ν3 band of CH 3D

Abstract

Using a tunable diode-laser spectrometer, we have measured at room temperature the H 2-broadening coefficients of 12 CH 3 D for 36 lines belonging to QP and QR branches in the ν 3 parallel band. The recorded lines with J values ranging from 1 to 15 and K from 0 to 9 ( K⩽ J) are located between 1196 and 1412 cm −1. The H 2-broadening coefficients were determined by fitting each spectral line with Voigt, Rautian, and Galatry profiles. They were also calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the weak electrostatic contributions the atom–atom Lennard-Jones potential. The theoretical results are in reasonable agreement with the experimental data, except for high J transitions where they are overestimated and for K approaching or equal to J with J⩾3 where they are underestimated. The latter discrepancy may be caused by the assumption to consider only Δ K=0 collision-induced transitions, associated with |Δ J| transitions up to 4.