A study of the methane catalyzed isomerization of HCO+ to HOC+ and the elimination of methane from metastable methoxymethyl cation

Eur. J. Mass Spectrom. 10, 747–754 (2004)
DOI: 10.1255/ejms.683

A study of the methane catalyzed isomerization of HCO⁺ to HOC⁺ and the elimination of methane from metastable methoxymethyl cation

Travis D. Fridgen^*
Department of Chemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5
John L. Holmes
Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada, K1N 6N5

ABSTRACT:

Electronic structure calculations on the methane catalyzed HCO⁺/HOC⁺ potential energy surface have been conducted. The results show that 1,2-proton transfer from C to O can be efficiently catalyzed by CH₄. The complex CH₄/HCO⁺ and the closely related species, CH₅⁺/CO, are separated from the methoxymethyl cation CH₃OCH₂⁺ by a large potential energy barrier. It follows from the calculations that the metastable methoxymethyl cation is very unlikely to dissociate to yield HOC⁺. New experiments also show that HOC⁺ is not produced to any observable extent. A new explanation is proposed for the composite peak for m/z 29 observed from metastable dissociation of metastable methoxymethyl cation. The two components both arise from the formation of HCO⁺, but via different transition states. The minor, narrow, component involves dissociation from the CH₅⁺/CO complex and the broad peak from the CH₄/HCO⁺ ion-molecule complex.

Keywords: formyl cation, proton-transport catalysis, HOC⁺, metastable dissociaiton, computational chemistry, potential energy surface, methoxymethyl cation, isomerization

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