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 sectio ns for OH+/OD+ derived from O+ and H2O/D2O collisions over the range o f 0.25-20 eV relative energy. The cross sections for the isotopic homo logues have the same form, a bimodal behavior that appears to be relat ed to the thermochemical thresholds for two reaction channels that giv e rise to OH+/OD+. The analysis of time-of-flight (TOF) measurements, based on the osculating complex model, is compared to phase-space theo ry calculations. The results indicate that the low-energy channel invo lves atom transfer via an orbiting complex. The high-energy feature ap pears to be associated with the opening of the OH+/OD+ + OH/OD A(2) Si gma(+) channel.