Dissociative Photodetachment Dynamics of the OH(CH) Anion Complex.

Photoelectron-photofragment coincidence (PPC) measurements on OH(CH) anions at a photon energy of 3.20 eV revealed stable and dissociative photodetachment product channels, OH-CH + e and OH + CH + e, respectively. The main product channel observed was dissociation to the reactants (>67%), OH + CH ( = 0, 1, 2) + e, where vibrational excitation in the C-H stretching modes of the CH photofragments corresponds to a minor channel. The low kinetic energy release (KER) of the dissociating fragments is consistent with weak repulsion between the OH + CH reactants near the transition state as well as the partitioning of energy into rotation of the dissociation products. An impulsive model was used to account for rotational energy partitioning in the dissociative photodetachment (DPD) process and showed good agreement with the experimental results. The low KER of the dissociating fragments and the similarities in the photoelectron spectra between stable and dissociative events support a mechanism involving the van der Waals complex formed upon photodetachment of OH(CH) as an intermediate in the dominant OH + CH + e dissociative channel.