Laser photolysis, infrared fluorescence determination of methyl(.nu.3) vibrational deactivation by helium, argon, nitrogen, carbon monoxide, sulfur hexafluoride, and acetone

Abstract

Room temperature vibrational deactivation rate constants are reported for methyl radicals with antisymmetric stretch excitation, CH3(nu3) + M CH3 + M, where M = He, Ar, N2, CO, SF6, (CH3)2CO. Excimer laser photolysis of acetone at 193 nm is used to populate CH3(nu3), and time-resolved infrared emission from the CH stretch is used to follow the deactivation kinetics. The rate constants obtained are (+/-2sigma) (2.6 +/- 0.5) x 10 T (He, (6.8 +/- 0.7) x 10 T (Ar), (6.1 +/- 0.6) x 10 T (N2), (3.6 +/- 0.7) x 10 T (CO), (6.9 +/- 0.7) x 10 T (SF6), and (8.1 +/- 0.9) x 10 S (CH3COCH3) in units of cmT molecule s . The deactivation probability is not controlled by long-range forces due to the lone electron on the radical, but rather by the probabilities for intramode vibrational energy flow in CH3.