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 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 < or = 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.

OH-H2 entrance channel complexes.

The entrance channel to the OH+H2-->H2O+H hydrogen abstraction reaction has been investigated from several different experimental approaches and complementary theoretical calculations. Weakly bound complexes between the hydroxyl radical and molecular hydrogen have been stabilized within a shallow well in the entrance channel and characterized via electronic spectroscopy on the OH A2Sigma+-X2Pi transition. Laser-induced fluorescence and fluorescence depletion experiments have revealed the binding energy of H2/D2 with ground state OH X2Pi radicals, the intermolecular energy levels supported by the OH A2Sigma+ (v'=0,1)+H2/D2 potential, and the OH-H2/D2 excited state dissociation limit. The OH X2Pi + H2 potentials have also been examined through inelastic scattering measurements on Lambda-doublet state-selected OH with normal or para-H2. Finally, photodetachment of an electron from the H3O- anion enabled the neutral reaction to be probed in conformations sampled by the two isomeric forms of the anion.