Diode-Laser Measurements of He-Broadening Coefficients in the ν6Band of12CH3F

He-broadening coefficients are measured for 28 lines of12CH3F in theRQ0(Ki= 0, ΔK= 1, ΔJ= 0) andRQ6(Ki= 6, ΔK= 1, ΔJ= 0) branches of the ν6band, using a tunable diode laser spectrometer. The collisional widths obtained by fitting Rautian profiles to the measured shapes of the lines are slightly larger than those derived from Voigt profiles. The broadening coefficients for the lines belonging to the same lowJtransitions are significantly greater in theRQ0branch than in theRQ6branch. Moreover, they decrease on the whole with increasingJin theRQ0branch and tend to increase fromJvarying from 7 to 10 in theRQ6branch. These trends may be approximately reproduced by calculations based on a semiclassical impact theory of collisional broadening.