Reaction and Quenching of Cl(²Pj) Atoms in Collisions with Methane and Deuterated Methanes

Bimolecular rate constants for the reaction of ground-state Cl( 2 P 3/2 ) atoms and for quenching of excited spin−orbit state Cl*( 2 P 1/2 ) atoms in collisions with CH 4, CD 4, and CH 2 D 2 have been measured at room temperature. Chlorine atoms were produced by the photolysis of CCl 2 F 2 and HCl at 193 nm and monitored by the technique of laser-induced fluorescence at the vacuum ultraviolet region. The rate constants for the reaction of Cl atoms were found to be as follows: CH 4, (10.0 ± 1.0) × 10 -14; CH 2 D 2, (7.0 ± 0.8) × 10 -14; and CD 4, (8.2 ± 1.0) × 10 -15 cm 3 molecule -1 s -1 . The absolute second-order rate constants for the removal of Cl* atoms were as follows: CH 4, (3.0 ± 0.3) × 10 -11; CH 2 D 2, (1.1 ± 0.1) × 10 -10; and CO 2, (1.2 ± 0.1) × 10 -11 cm 3 molecule -1 s -1 . The removal of Cl* atoms was shown to proceed mainly by collisional quenching.