The C2H7+ potential energy surface: a Fourier transform ion cyclotron resonance investigation of the reaction of methyl cation with methane

Fourier transform ion cyclotron resonance experiments have been carried out to probe the nature of the potential energy surface for the reaction of me thyl cation (CH+3) with methane (CH4) to give the ethyl cation (C2H5+). Pro duct distributions for reactions of CH+3 and CD+3 with CD4 and CH4, respect ively, are found to give a near statistical distribution of ethyl cation pr oducts, in good agreement with previous work. When the methyl cation is ini tially coordinated to HF in the form of a methylfluoronium ion, however, th e product distributions are decidedly nonstatistical and an indicative of a reaction which is very nearly thermoneutral. Thermochemical data for relev ant species suggest that the reaction is very slightly endothermic. All of the experiments support the intermediacy of a C2H+7 complex in the reaction s. Ab initio calculations, in conjunction with all of the experimental data , reveal that there are likely three different stable forms of C2H+7 involv ed in the potential energy surface for the reaction. One of the forms, a no nclassical C2H+5 coordinated to H-2 in a proton bound dimerlike structure, has not previously been considered to play a role in this reaction. The exi stence of this structure is supported by infrared multiphoton dissociation experiments on C2H+7 previously carried out by Lee and co-workers (J. Am. C hem, Sec. 111 (1989) 5597) and the high pressure mass spectrometric experim ents of Hiraoka and Kebrule (J. Am. Chem. Sec. 98 (1976) 6119). (C) 2000 El sevier Science B.V.