Vibrational Spectroscopy of Intermediates in Methane-to-Methanol Conversion by FeO+

Gas phase FeO+ can convert methane to methanol under thermal conditions. Two key intermediates of this reaction are the [HO-Fe-CH3](+) insertion intermediate and Fe+(CH3OH) exit channel complex. These intermediates are selectively formed by reaction of laser-ablated Fe+ with organic precursors under specific source conditions and are cooled in a supersonic expansion. Vibrational spectra of the sextet and quartet states of the intermediates in the O-H and C-H stretching regions are measured by infrared multiple photon dissociation of Fe+(CH3OH) and [HO-Fe-CH3](+) and by monitoring argon atom loss following irradiation of Fe+(CH3OH)(Ar) and [HO-Fe-CH3](+)(Ar)(n) (n = 1, 2). Analysis of the experimental results is aided by comparison with hybrid density functional theory computed frequencies. Also, an improved potential energy surface for the FeO- + CH4 reaction is developed based on CCSD(T) and CBS-QB3 calculations for the reactants, intermediates, transition states, and products.