INTERATOMIC POTENTIALS FOR EXCITED-STATES OF XEHE AND XEAR

Interatomic potentials for the interaction of low-lying excited states of Xe(5p5nl) (nl = 6s,6p,5d) with He and Ar have been calculated. A novel method has been developed that refines and extends the results of ab initio electronic structure calculations by incorporating available spectroscopic information using a model Hamiltonian. The ab initio calculations treat the heavy-atom cores using relativistic effective potentials and include spin-orbit effects at the configuration-interaction level. The model Hamiltonian depends on a small number of physically sensible parameters, some of which are extracted from the ab initio calculations, and others of which are determined more accurately from spectroscopy. The model Hamiltonian is then used to recalculate the potential curves and coupling matrix elements. The results obtained have significant implications for two classes of recent experiments. Recent measurements of rate constants for state-to-state transitions of Xe* induced by collisions with He or Ar have revealed that the magnitude of the rate depends strongly on the specific transition and collision partner. The present adiabatic potential curves exhibit several regions of strong coupling, which can be associated with the crossings of "diabatic states," and which can be correlated with those transition rates found to be large. Other experiments have measured multiphoton ionization spectra of XeAr, thereby providing information on the vibrational levels of the excited-state potentials that can be compared with the present calculations.