The room temperature conversion of gaseous methanol to carbon monoxide and hydrogen on a polycrystalline Au film at ambient pressure has been triggered and characterized by oxygen K-edge excitation and vibrationally resolved resonant inelastic X-ray scattering. The rate-limiting first methanol dehydrogenation step is driven by ultrafast O-H dissociation and deprotonation of O K-edge excited CH₃OH. The Au surface further dehydrogenates the CH₃O⁺ photoradical created by X-rays via electron transfer from the Au surface. With vibrationally resolved resonant inelastic X-ray scattering, we trace the CO molecular potential energy surface along the C-O coordinate. The CO bond softens, and the C-O stretch frequency changes from 2250 to 2065 cm^-1 at a CO chemisorption energy of 38-58 kJ/mol. This constitutes weak chemisorption as compared to the transition metals but also stronger bonding than the physisorbed CO species on single-crystal Au surfaces. In liquid methanol, the recombination of the CH₃O⁺ photoradical created by X-rays with protons quenches this conversion.