A systematic quantum chemical investigation of the C-H bond activation in methane by gas phase vanadium oxide cation VO+

The interaction between a methane molecule and the VO(+) cation in the gas phase has been investigated by means of single reference density functional (B3LYP) and wave function-based multireference (MR) correlation calculations. For the latter, an extrapolation technique is used to evaluate correlation energies at the basis set limit. A comprehensive picture for the C-H activation features a variety of molecular structures corresponding to both minima and transition states. Possible reaction paths are discussed, also taking into account change of the spin multiplicity. Activation of the methane molecule by VO(+) is always an endothermic process. Competing reaction paths might be expected. An evaluation of miscellaneous computational methods is performed using calculated energy differences for various molecular structures. Results obtained from the MR calculations exhibit no systematic convergence with increasing size of the active space used, and for two largest active spaces relative energies still differ by up to 25 kJ/mol. Simple mean difference between the B3LYP results and the best MR values is -50 +/- 19 kJ/mol.