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.