Computational study of the reaction between CH4 and CH +4

Abstract

A CNDO programme has been developed for dealing with systems containing only carbon and hydrogen (NABG). The parametrization adopted by Fischer and Kollmar was used since it is capable of dealing with charged molecules. The programme was written to allow the investigation of odd-electron systems. Furthermore, incorporated into the programme is a minimization routine in which all the molecular parameters of any molecular system can be varied. The reaction, CH₄+ CH⁺₄= CH⁺₅+ CH₃· has been studied in detail.

The calculations suggest that the entity C₂H⁺₈, a postulated intermediate, has an electronic binding energy almost equal to that of the free CH₄ and CH⁺₄. The exothermicity of the reaction has been calculated to be 8.3 kcal mol^–1. (expt. value = 9.2 ± ? kcal mol^–1). The movement of the atomic centres during the process of the reaction has been calculated and was found largely to reflect intuitive chemical ideas. These calculations enable one effectively to “see” the reaction occurring by the diagrammatic representation of various stages in it. There is no significant movement of the atomic centres from the positions in the free ion and molecule until the two carbon centres are about 3.6 Å apart, thus dispelling any notions of a reaction at long range.