Probing reactive potential energy surfaces by vibrational activation of H-2-OH entrance channel complexes

This review article presents an overview of recent experimental and theoret ical studies of reactant complexes composed of OH and H-2 that have been st abilized in the entrance channel to the OH + H-2 --> H2O + H hydrogen abstr action reaction. The first part focuses on infrared and stimulated Raman sp ectroscopic measurements of H-2-OH complexes with particular emphasis on ch aracterizing the bound states supported by the intermolecular well in the e ntrance channel. The experimental vibrational spectra are compared with fir st principles quantum calculations to assign the observed intermolecular le vels and quantify the degree of body-fixed orientation achievable within th e reactant complex. The second part explores the lifetime and inelastic sca ttering dynamics of vibrationally activated H-2-OH upon OH and H-2 stretchi ng excitation. The half-collision dynamics, which sample a restricted range of initial orientations in the H-2-OH complex, provide complementary infor mation to full-collision studies of reactive and inelastic scattering dynam ics of OH + H-2, and direct comparisons are made between the various studie s. The article concludes by summarizing some of the remaining questions abo ut the decay dynamics of vibrationally activated H-2-OH entrance channel co mplexes that require further experimental and theoretical work.