Relativistic study of vuv radiation properties from Kr-Xe gas mixtures

Abstract

In an effort to obtain a microscopic understanding of the origin of vuv emission from inert heavy-atom gas mixtures we present results from relativistic calculations of the krypton-xenon spectrum in the 68 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ region. Calculations carried out on the interatomic interaction in the ground and in the low-lying spin-orbit excited states $[{0}^{\ensuremath{-}}{(}^{3}{P}_{2}),{0}^{+}{(}^{3}{P}_{1}),{1(}^{3}{P}_{1}),{1(}^{3}{P}_{2}),{2(}^{3}{P}_{1})]$ of the krypton-xenon dimer are presented. The calculations were executed in a two-step procedure in which the CCSD(T) model for the ground state and the CCSD response theory model for the excited states were used to obtain spin-free potential curves in the first step. A perturbational treatment of the spin-orbit interaction within the atomic mean-field approximation was applied in the next step. Large-core quasirelativistic effective core potentials with richly augmented valence basis sets and midbond functions were used. All calculations were corrected for basis set superposition errors by applying the counterpoise method. For all involved states, spin-orbit perturbed potential energy curves were computed and equilibrium geometries, potential well depths, and local extrema were determined. Vibrational analysis and Franck-Condon factors for the ground and ${0}^{+}{(}^{3}{P}_{1}{),1(}^{3}{P}_{1})$ states were also calculated. The geometry dependence of the electronic dipole transition matrix elements between all involved excited states and the ground state was investigated. Excitation energies and potentials were obtained that are in excellent agreement with results based on fitting to experimental data. Out of some earlier disparate experimental assignments of the character of the excited states of the KrXe complex, the present results adhere most closely to the ones presented by Pibel et al. [J. Chem. Phys. 101, 10 242 (1994)]. Analyzed together with the experimental data, the theoretical results provide a clear picture of the organization of exciplex states and of the origin of strong vuv emission from these states that follows from binary collisions of the heavy inert Kr and Xe atoms.