Calculations of fine-structure changing collisions of excited Xe

Calculations of cross sections for mixing of Xe(5p{sup 5}nl)(nl=6s,6p,5d) by thermal collisions with He and Ar are reported. Ab initio structure calculations have been performed using the COLUMBUS codes, which include spin orbit effects and relativistic effects in the heavy atom core. A model Hamiltonian approach has been developed that allows the necessary nonadiabatic coupling matrix elements to be determined. The dynamics equations are solved using the coupled channel method, and calculated mixing rates are compared with recent experiments. The mixing rates depend strongly on the particular transition and on the collision partner (He or Ar). The calculations provide an explanation for most of the state-to-state rates in terms of the features of the potential curves.