A guided-ion-beam mass spectrometer is used to study the reactions of Co+ + CD4 and CoCH2+ + D2 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 £>o(Co+-CD) = 422 ± 37 kJ/mol and Dq(Co+-C) = 347 ± 29 kJ/mol. We also find extensive hydrogen scrambling in the CoCH2+ + D2 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.

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The potential energy surface for the CoC2H6 + system is probed by using a guided-ion beam tandem mass spectrometer in conjunction with a dc discharge/flow tube ion source. Bimolecular reactions of Co+ + C2H6, Co+(C2H4) + H2 (D2), and CoCH2 + + CH4 (CD4) are examined, as well as threshold collisional activation of Co+(C2H6) and Co+(C2H4) with Xe. The results allow details of the [CoC2H6]+ potential energy surface (PES) to be elucidated. Key features of the PES include barrier heights of 1.04 ± 0.11 eV (0.29 ± 0.09 eV in excess of the endothermicity) for the reaction of Co+ with ethane to form CoCH2 + + CH4 and of 0.32 ± 0.12 eV for the exothermic reaction to form Co+(C2H4) + H2. From the collisional activation studies, we determine 0 K bond dissociation energies for Co+−C2H4 and Co+−C2H6 complexes of 1.86 ± 0.07 and 1.04 ± 0.05 eV, respectively, in good agreement with literature values. D 0(DCo+−C2H4) = 1.13 ± 0.16 eV is also determined although it is somewhat more speculative.