TRANSITION-STATE SPECTROSCOPY OF THE OH-2-]H2O+H REACTION VIA PHOTODETACHMENT OF H3O- AND D3O-(H)

The transition state region of the reaction OH + H-2 --> H2O + H is in vestigated by photoelectron spectroscopy of the H3O- and D3O- anions. The peaks observed in the spectra are from a combination of vibrationa l progressions and overlapping anion --> neutral electronic transition s. The photoelectron angular distributions indicate that two processes contribute to the spectra; these are assigned to photodetachment from the H-(H2O) and OH-(H-2) forms of the anion. A comparison of experime nts performed in two different laboratories shows that the two forms o f the ion readily interconvert and that the relative populations are d etermined solely by the temperature of the ions. To interpret the spec tra, a two-dimensional ab initio potential energy surface for the anio n was constructed, wave functions for the first few vibrational levels were determined, and the photoelectron spectra were simulated using t he Walch-Dunning-Schatz-Elgersma surface for the OH + H-2 reaction. A comparison of the experimental and simulated spectra showed that photo detachment from the v = 0 level of the anion, which is localized in th e H-(H2O) well, primarily probes the H + H2O exit valley of the neutra l surface. The v = 2 level of the anion is the first with significant amplitude in the OH-(H-2) well, and photodetachment from this level pr obes the OH + H-2 transition state region. The simulated spectra are i n qualitative agreement with the experimental spectra but do indicate that the neutral reactive surface needs to be modified.