Pressure broadening of transitions in the CH3F ν4 band using Stark modulated Lamb dips

A cw-OPO laser system has been used to measure pressure broadening coefficients for the ν4 vibration–rotation transitions of CH3F by using Stark modulated Lamb dips. Eight pressure coefficients were determined from various pressure data, where each line shape was fitted to the Lorentzian function. The rQ(1,0) coefficient was found to be largely different from that of rR(0,0), where the upper states of both transitions have the same J and K values but different parities of the l-type doublet. The coefficient for rQ(7,4) obtained in the present study agrees with that obtained by a Voigt profile analysis (Cartlidge and Butcher, 1990).