A study of isotope effects in the reaction O+ + H2O/D2O → OH+/OD+ + OH/OD using guided-ion beams

Guided-ion beam methods were used to measure the absolute cross sections for OH+/OD+ derived from O+ and H2O/D2O collisions over the range of 0.25–20 eV relative energy. The cross sections for the isotopic homologues have the same form, a bimodal behavior that appears to be related to the thermochemical thresholds for two reaction channels that give rise to OH+/OD+. The analysis of time-of-flight (TOF) measurements, based on the osculating complex model, is compared to phase-space theory calculations. The results indicate that the low-energy channel involves atom transfer via an orbiting complex. The high-energy feature appears to be associated with the opening of the OH+/OD+ + OH/OD A2Σ+ channel.