Observation and analysis of optical free induction decay in the CH3F Ν4 band

Abstract Optical free induction decay (FID) signals of the CH 3 F ν 4 band were observed by using a cw-OPO infrared laser coupled with a Stark switching method. The observed signals have been Fourier transformed to obtain the Lorentz functions and the widths have been analyzed to determine the pressure-broadening coefficients for r R(0,0), r Q(1,0), r R(1,0), r R(1,1), and p P(2,1) to be 1/(π T 2 p ) = (46.1 ± 2.1), (31.6 ± 3.6), (21.8 ± 2.5), (25.2 ± 4.0), and (26.5 ± 1.8) MHz/Torr, where T 2 is the transverse decay time. The value of r R(0,0) is larger than that determined from a recent pressure-broadening measurement by 39 ± 12%. The difference is explained by collision induced reorienting transitions (Δ M  = ±1, ΔJ = 0).