Spectroscopy of the transition state: Elementary reactions of the hydroxyl radical studied by photoelectron spectroscopy of O−(H2O) and H3O−2

The transition state regions of the OH+OH→O(3P)+H2O and the OH+H2O→H2O+OH reactions are studied by photoelectron spectroscopy of the O−(H2O) and H3O−2 anions and their deuterated analogs. The spectra show resolved vibrational progressions attributed to H-atom vibrational motion in the unstable neutral complexes formed by photodetachment. The positions and intensities of the peaks change markedly upon isotopic substitution. One-dimensional Franck–Condon calculations using ab initio potentials for the anion and neutral are used to interpret the peak spacings and intensities, as well as the strong isotopic effects. The results are discussed in the context of previously obtained transition state spectra for heavy+light–heavy reactions.