Probing reactive potential energy surfaces by vibrational activation of H2-OH entrance channel complexes

This review article presents an overview of recent experimental and theoretical studies of reactant complexes composed of OH and H-2 that have been stabilized in the entrance channel to the OH + H-2 --> H2O + H hydrogen abstraction reaction. The first part focuses on infrared and stimulated Raman spectroscopic measurements of H-2-OH complexes with particular emphasis on characterizing the bound states supported by the intermolecular well in the entrance channel. The experimental vibrational spectra are compared with first principles quantum calculations to assign the observed intermolecular levels and quantify the degree of body-fixed orientation achievable within the reactant complex. The second part explores the lifetime and inelastic scattering dynamics of vibrationally activated H-2-OH upon OH and H-2 stretching excitation. The half-collision dynamics, which sample a restricted range of initial orientations in the H-2-OH complex, provide complementary information to full-collision studies of reactive and inelastic scattering dynamics of OH + H-2, and direct comparisons are made between the various studies. The article concludes by summarizing some of the remaining questions about the decay dynamics of vibrationally activated H-2-OH entrance channel complexes that require further experimental and theoretical work.