Ion–molecule reaction mechanisms: Thermal energy gas phase reactions of 12C+ and 13C+ ions with CH4, C2H4, C2H6, C3H6, C3H8, and CD3CH2CD3

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Abstract
The results of a tandem Dempster–ICR mass spectrometric study of carbon ion reactions with several hydrocarbons are reported. The reactions of ground state (2P) 12C+ and 13C+ ions at near thermal translational energies (0.1 eV) with methane, ethylene, ethane, propylene, propane, and propane 1,1,1,3,3,3‐d6 were investigated. Reaction branching ratios show several reactions with varying degrees of 13C insertion in the ionic products. On progression from smaller to larger neutral reactants the results are characterized by less retention of the reactant ion nucleus in the ionic products. Reaction of C+ with methane gives a product distribution in line with that predicted by Quasiequilibrium Theory (QET) for excited C2H4+ species. However, propylene shows little correlation with QET predictions. Moreover, 13C+ reactions with ethane and propane exhibit reaction channels in which 13C retention in the ionic products is considerably greater than predicted from statistical considerations. It is concluded that the results are best rationalized by a combination of direct processes and an indirect mechanism involving C+ insertion at a C–H bond.

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