Dissociative Photodetachment Studies of Cooled HOCO- Anions Revealing Dissociation Below the Barrier to H + CO2

Dissociative photodetachment of internally cold HOCO- has been performed in a new cryogenically cooled photoelectron-photofragment coincidence apparatus, characterizing the HOCO potential energy surface in the Franck-Condon region determined by the anion. Three processes are observed in three distinct regions of this surface detachment to stable HOCO, dissociative photodetachment to OH+CO and dissociative photodetachment to H+CO2. Relative to earlier work on internally hot anions the H + CO2 channel is significantly enhanced, with efficient dissociation to H + CO2 unambiguously detected below calculated barriers in the OH + CO -> H + CO2 reaction. This finding shows that an important low-energy pathway exists to the exit-channel in this reaction reinforcing the need for further refinement of this important potential energy surface and providing benchmarks for further theoretical efforts.