Electronic and vibrational spectroscopy of intermediates in methane-to-methanol conversion by CoO+

At room temperature, cobalt oxide cations directly convert methane to methanol with high selectivity but very low efficiency. Two potential intermediates of this reaction, the [HO-Co-CH3](+) insertion intermediate and [H2O-Co=CH2](+) aquo-carbene complex are produced in a laser ablation source and characterized by electronic and vibrational spectroscopy. Reaction of laser-ablated cobalt cations with different organic precursors seeded in a carrier gas produces the intermediates, which subsequently expand into vacuum and cool. Ions are extracted into a time-of-flight mass spectrometer and spectra are measured via photofragment spectroscopy. Photodissociation of [HO-Co-CH3](+) in the visible and via infrared multiple photon dissociation (IRMPD) makes only Co+ + CH3OH, while photodissociation of [H2O-Co=CH2](+) produces CoCH2+ + H2O. The electronic spectrum of [HO-Co-CH3](+) shows progressions in the excited state Co-C stretch (335 cm(-1)) and O-Co-C bend (90 cm(-1)); the IRMPD spectrum gives nu(OH) = 3630 cm(-1). The [HO-Co-CH3](+)(Ar) complex has been synthesized and its vibrational spectrum measured in the O-H stretching region. The resulting spectrum is sharper than that obtained via IRMPD and gives nu OH = 3642 cm(-1). Also, an improved potential energy surface for the reaction of CoO+ with methane has been developed using single point energies calculated by the CBS-QB3 method for reactants, intermediates, transition states and products. (C) 2011 American Institute of Physics. [doi:10.1063/1.3626412]