Mapping the OH+CO -> HOCO reaction pathway through IR spectroscopy of the OH-CO reactant complex

A hydrogen-bonded complex composed of the OH and CO reactants has been iden tified 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 prob e portions of the reaction path leading to HOCO. The spectroscopic measurem ents have accessed highly excited intermolecular levels, with energies up t o 250 cm(-1) above the zero-point level, which lie in close proximity to th e transition state for reaction. The OH-CO binding energy, D-0 less than or equal to 430 cm(-1), has also been established from the quantum state dist ribution of the OH fragments following vibrational predissociation of the O H-CO complex. Complementary electronic structure calculations have been per formed to characterize the OH-CO and OH-OC complexes, the transition state for HOCO formation, and the direct reaction path that connects the experime ntally observed OH-CO complex to the HOCO intermediate.