Ab initio spin-coupled description of the reactions CH2(1A1) + H2 .fwdarw. CH4 and CH4 .fwdarw. CH3(2A1') + H

Abstract

Spin-coupled theory, which represents the modern development of valence bond theory, is applied to the singlet methylene insertion reaction CH{sub 2}({sup 1}A{sub 1}) + H{sub 2} {yields} CH{sub 4} and to the hydrogen atom abstraction reaction CH{sub 4} {yields} CH{sub 3}({sup 2}A{sub 1}{prime}) + H. The spin-coupled wave function provides a highly visual model of the behavior of correlated electrons. Concepts such as directed covalent bonds, formed from the overlap of sp{sub x}-like hybrids on carbon and 1s functions on hydrogen, are shown to arise naturally from minimizing the total energy without preconceptions. There are, however, some important differences from the ideas of classical VB theory. A new non-least-motion pathway with no activation barrier is proposed for the singlet methylene insertion reaction.