The dynamics of the H-atom abstraction reactions between chlorine atoms and the methyl halides

Abstract

Abstract The rotational state distributions of nascent HCl( v ′ =0) products of the reactions between ground spin–orbit state Cl( 2 P 3/2 ) atoms and CH 4 and CH 3 X (X=F, Cl, Br, I) molecules are reported. Reactions were initiated by photolysis of molecular chlorine at 355 nm and the nascent HCl( v ′ =0) products were probed using 2 + 1 resonance-enhanced multiphoton ionization in a time-of-flight mass spectrometer. In accord with previous measurements, the HCl( v ′ =0) products for the Cl + CH 4 reaction are rotationally very cold. A much greater degree of rotational excitation is observed in the HCl( v ′ =0) products of the reactions involving the methyl halides, which increases such that CH 3 I 3 Br 3 Cl 3 F, correlating with the magnitudes of the dipole moments of the radical fragment co-products. Ab initio calculations were performed at the G2//MP2/6-311G(d,p) level to characterize molecular complexes and transition states on the reaction pathways for all the reactions studied except Cl + CH 3 I. All proceed over barriers and have weakly bound complexes in the pre- and post-transition state regions of the potential energy surfaces. Comparisons are drawn between the dynamics of these reactions and those of Cl atoms with other organic molecules containing heteroatoms.