Fine structure effects in the O+‐O collision frequency

Abstract

Effects of the fine structure of atomic oxygen on the O+‐O ion‐neutral momentum transfer collision frequency νin are investigated to assess whether they could account for persistent discrepancies between theoretical calculations and values of νin determined from observations. Potential curves for the molecule have been calculated that include spin‐orbit effects and properly dissociate to the three asymptotic limits O+‐O(³PJ) (J=2,1,0). Coupled channel scattering calculations have been performed to determine νin. The results show that νin depends strongly on the initial fine structure level, and the average over a thermal distribution of initial states is a few percent smaller than recent theoretical calculations that neglect fine structure effects. The most recent analysis of observations leads to values of νin about 30% smaller than older values. The theoretical calculations are now consistent with the most recent experimental determinations of νin.