The electronic structure of rare gas halide excimers

Abstract

The rare gas halide excimer states are analyzed in terms of an electrostatic model that includes mixing between the ionic excimer and neutral ground configurations. The energy splitting between the 2Σ and 2Π excimer states is strongly affected by this configuration mixing. A Rittner type energy expression is derived and parameterized for the KrF* excimer energy curves, which are found in good agreement with the ab initio curves of Dunning and Hay. Perturbation expressions are also derived for the dipole and transition moments of this system. The long-range formulas are compared with the available ab initio literature. These expressions are then applied to a qualitative analysis of the transition moments of KrF*. The 2Σ+→2Σ+ transition is found to be dominant, in agreement with the ab initio results. The transition moment can actually be viewed as a small admixture of the large ionic dipole moment. Since the dipole moment varies as R and the mixing coefficient as exp(−αR), it is apparent that the transition moment will vary rapidly as a function of R and also of the vibrational quantum number.