Methane to Methanol Conversion Induced by Thorium Oxide through the CH3Th(O)H Intermediate in Solid Argon

Reactions of ThO molecules and CH4 have been investigated in solid argon near 4K. The CH3Th(O)H molecule is produced when the sample is exposed to UV irradiation. Identification of this new intermediate is substantiated by observation of the Th=O and Th-H stretching vibrational modes with isotopic substitution via matrix infrared spectroscopy, and the assignments are supported by electronic structure frequency calculations. Methanol absorptions increase together with formation of the CH3Th(O)H molecule, suggesting a methane to methanol conversion induced by thorium oxide proceeding through the CH3Th(O)H intermediate. The formation of CH3Th(O)H from ThO + CH4 is exothermic (Delta H-rxn = -11 kcal/mol) with an energy barrier of 30 kcal/mol at the CCSD(T)//B3LYP level. Decomposition of this intermediate to form methanol involves spin crossing, and the overall reaction from the intermediate is endothermic by 127 kcal/mol. There is no activation energy for the reaction of thorium atoms with methanol to give CH3Th(O)H, as observed in separate experiments with Th and CH3OH.