Calculation of the photodetachment spectrum for H3O-

The spectrum for the photodetachment of electrons from H3O- to produce H-2 + OH or H + H2O is calculated with the rotating bond approximation (RBA). This method treats explicitly three active degrees of freedom (two stretching vibrations and one bending mode) in both H3O- and the neutral reactive product. Potential-energy surfaces based on new ab initio calculations in these same three degrees of freedom are used. Comparison with experimental photodetachment spectra demonstrates the accuracy of the model and confirms that the experiment accesses photodetachment from both the H-(H2O) isomer of H3O-, producing H + H2O, and the higher energy OH-(H-2) isomer yielding OH + H-2. In the latter case, a progression of bands associated with different OH rotational states in the H-2 + OH product channel is predicted. The calculations suggest that the observed photodetachment spectrum is mainly providing information on the entrance and exit channels of the OH + H-2 --> H2O + H potential-energy surface quite close to the transition state.