State selected ion–molecule reactions by a TESICO technique. XII. Internal energy dependence of the relative cross section and mechanism branching of the reaction CH+4(v) +CH4 →CH+5 +CH3 and its isotopic variants

Total cross sections of the title reaction studied at collision energies 0.6–3 eV by the TESICO method were found to decrease by about 1.6 times as the internal energy of the reactant ion is increased from 0.1 to 1 eV. Branching ratios of collisional mechanisms were derived from isotope labeling studies: with decreasing total initial energy (sum of collision energy and reactant ion internal energy) from 4 to 0.9 eV the fraction of the dominant proton transfer mechanism slightly decreases, the fraction of H-atom transfer is almost constant, and the fraction of intermediate complex formation increases from about 5% to 15%. Significant isotope effects were observed in the impulsive proton and H-atom transfer mechanisms depending on whether the transferred particle was H or D. The charge transfer channel represents about 10%–50% of the chemical reaction channel.