DIODE-LASER MEASUREMENTS OF HE-BROADENING COEFFICIENTS IN THE NU(6) BAND OF (CH3F)-C-12

He-broadening coefficients are measured for 28 lines of (CH3F)-C-12 in the (R)Q(0) (K-i = 0, Delta K = 1, Delta J = 0) and (R)Q(6) (K-i = 6, Delta K = 1, Delta J = 0) branches of the nu(6) band, using a tunable diode laser spectrometer. The collisional widths obtained by fitting Rautian profiles to the measured shapes of the lines are slightly larg er than those derived from Voigt profiles. The broadening coefficients for the lines belonging to the same low J transitions are significant ly greater in the (R)Q(0) branch than in the (R)Q(6) branch. Moreover, they decrease on the whole with increasing J in the (R)Q(0) branch an d tend to increase from J varying from 7 to 10 in the (R)Q(6) branch. These trends may be approximately reproduced by calculations based on a semiclassical impact theory of collisional broadening. (C) 1997 Acad emic Press.