The gas-phase reaction mechanism between methane and rhodium monoxide for the formation of methanol, syngas, formaldehyde, water, and methyl radical have been studied in detail on the doublet and quartet state potential energy surfaces at the CCSD(T)/6-311+G(2d, 2p), SDD//B3LYP/6-311+G(2d, 2p), SDD level. Over the 300-1100 K temperature range, the branching ratio for the Rh((4)F) + CH(3)OH channel is 97.5-100%, whereas the branching ratio for the D-CH(2)ORh + H(2) channel is 0.0-2.5%, and the branching ratio for the D-CH(2)ORh + H(2) channel is so small to be ruled out. The minimum energy reaction pathway for the main product methanol formation involving two spin inversions prefers to both start and terminate on the ground quartet state, where the ground doublet intermediate CH(3)RhOH is energetically preferred, and its formation rate constant over the 300-1100 K temperature range is fitted by k(CH3RhOH) = 7.03 x 10(6) exp(-69.484/RT) dm(3) mol(-1) s(-1). On the other hand, the main products shall be Rh + CH(3)OH in the reactions of RhO + CH(4), CH(2)ORh + H(2), Rh + CO +2H(2), and RhCH(2) + H(2)O, whereas the main products shall be CH(2)ORh + H(2) in the reaction of Rh + CH(3)OH. Meanwhile, the doublet intermediates H(2)RhOCH(2) and CH(3)RhOH are predicted to be energetically favored in the reactions of Rh + CH(3)OH and CH(2)ORh + H(2) and in the reaction of RhCH(2) + H(2)O, respectively.
2009 Wiley Periodicals, Inc.