Heliomethonium dication, CH4He2+

Ab initio calculations at the MP216-31G** and MP2/6-311 + G(2d,p) levels sh ow that heliomethonium dication, CH4He2+ 1 [Chemistry in Superacids, Part 4 3; for Part 42 see G.A. Olah, T. Heiner, G. Rasul, G.K.S. Prakash, J. Org. Chem. 63 (1998) 7993] is a stable minimum on its potential energy surface. Structure 1, isoelectronic with CH5+, has C-s symmetry with a two-electron three-center bond (2e-3c) binding the carbon and two hydrogen atoms. The di ssociation of CH4He2+ into CH3He+ and H+ and CH3+ and HeH+ were calculated to be exothermic by 96.6 and 138.5 kcal/mol, respectively. The deprotonatio n process, however, has a considerable kinetic barrier of 21.3 kcal/mol. Th e reaction of CH42+ and He might be a suitable way to generate 1 in the gas phase. (C) 1999 Elsevier Science B.V. All rights reserved.