THE POTENTIAL-ENERGY SURFACE FOR ACTIVATION OF METHANE BY CO+ - AN EXPERIMENTAL-STUDY

A guided-ion-beam mass spectrometer is used to study the reactions of Co+ + CD4 and CoCH2+ + D-2 and thereby experimentally probe the potential energy surface for activation of methane by Co+. The results obtained are compared to recent theoretical results and agree with the conclusion that dehydrogenation of methane by Co+ is hindered by a tight four-center transition state complex. The major discrepancy observed between experiment and theory is in the height of this barrier, which theory predicts is 96-109 kJ/mol versus our experimental result of 34 +/- 8 kJ/mol. The endothermicities of all reactions are measured and allow the determination of D-0(Co+-CD) = 422 +/- 37 kJ/mol and D-0(Co+-C) = 347 +/- 29 kJ/mol. We also find extensive hydrogen scrambling in the CoCH2+ + D-2 reaction, a result that is interpreted by using phase space theory to help understand how various features on the potential energy surface control branching ratios among the various channels observed.