CONVERSION OF CH4 TO CH3OH - REACTIONS OF COO+ WITH CH4 AND D-2, CO+ WITH CH3OD AND D2O, AND CO+(CH3OD) WITH XE

The mechanisms and energetics involved in the conversion of CH4 to CH3OH by CoO+ are examined by using guided ion beam mass spectrometry. The forward and reverse reactions, CoO+ + CH4 <-> Co+ + CH3OH, the collisional activation of Co+(CH3OH), and the related reactions, CoO+ + D-2 <-> Co+ + D2O, are studied. It is found that the oxidations of methane and D-2 by CoO+, both exothermic reactions, do not occur until overcoming activation barriers of 0.56 +/- 0.08 and 0.75 +/- 0.04 eV, respectively. The behavior of the forward and reverse reactions in both systems is consistent with reactions that proceed via the insertion intermediates R-Co+-OH, where R = CH3 or H. The barrier is probably attributable to a four-centered transition state associated with addition of RH across the CoO+ bond. In the Co+ + CH3OH system (where CH3OD labeled reactant is used), reactions explained by initial C-H and O-H activation are also observed. The reaction mechanisms and potential energy surfaces for these systems are derived and discussed. Phase space theory calculations are used to help verify these details for the CoO+ + D-2 system. Thermochemistry for several species including CoOH+, CoD+, CoH, CoCH3+, Co+(CH3OD), CoOCH3+, and possibly OCoCH3+ is derived from measurements of reaction thresholds.