A Study of the Methane Catalyzed Isomerization of HCO+ to HOC+ and the Elimination of Methane from Metastable Methoxymethyl Cation

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.