Communication: New insight into the barrier governing CO₂ formation from OH CO

Despite its relative simplicity, the role of tunneling in the reaction OH CO → H CO₂ has eluded the quantitative predictive powers of theoretical reaction dynamics. In this study a one-dimensional effective barrier to the formation of H CO₂ from the HOCO intermediate is directly extracted from dissociative photodetachment experiments on HOCO and DOCO. Comparison of this barrier to a computed minimum-energy barrier shows that tunneling deviates significantly from the calculated minimum-energy pathway, predicting product internal energy distributions that match those found in the experiment and tunneling lifetimes short enough to contribute significantly to the overall reaction. This barrier can be of direct use in kinetic and statistical models and aid in the further refinement of the potential energy surface and reaction dynamics calculations for this system.