Mapping the OH + CO → HOCO reaction pathway through IR spectroscopy of the OH–CO reactant complex

Abstract

A hydrogen-bonded complex composed of the OH and CO reactants has been identified along the OH + CO → HOCO reaction pathway. IR action spectroscopy in the OH overtone region has been used to examine the vibrational modes of the linear OH–CO complex, including intermolecular bending modes that probe portions of the reaction path leading to HOCO. The spectroscopic measurements have accessed highly excited intermolecular levels, with energies up to 250 cm⁻¹ above the zero-point level, which lie in close proximity to the transition state for reaction. The OH–CO binding energy, D₀⩽430 cm⁻¹, has also been established from the quantum state distribution of the OH fragments following vibrational predissociation of the OH–CO complex. Complementary electronic structure calculations have been performed to characterize the OH–CO and OH–OC complexes, the transition state for HOCO formation, and the direct reaction path that connects the experimentally observed OH–CO complex to the HOCO intermediate.