K-dependence of broadening coefficients for CH_3F-N_2 and for other systems involving a symmetric top molecule

摘要

The variations of N_2-broadeing coefficients of CH_3F with the rotational quantum number K have been studied in the v_2 and v_5 bands, using a diode-laser spectrometer. Four different line families with same J values rainging from 3 to 17, and same #DELTA#J and #DELTA#K values have been recorded in the spectral tange 1478-1573 cm~(-1). The collisional halfwidths are obtained by fitting Voigt and Rautian profiles to the measured shapes of the lines. A semi-classical calculation of the N_2 broadening has provided results that are in overall agreemetn with the experimental data. The general trend for the broadening coefficients belonging to the same J transiton is to decrease with increasing K;this decrease is more significant at low J than at high J values. A similar K behavior has been observe and predictedfor other binary systems: CH_3F self-perturbed or perturbed by O_2, He,Ar;CH_3D selfperturbed or perturbed by N_2,O_2.A different K behavior is observed for the broadening coefficients of a symmetric top molecule having an inversion motion such as NH_3.