Crystal-field model study of the xenon hexafluoride molecule. I. Energy levels and molecular geometry

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Abstract
A crystal field approach is used to examine theoretically the energy levels and wavefunctions for a gaseous xenon hexafluoride molecule. The electronic configurations used are 5s2, 5s5p, and 5p2 of hexavalent xenon. Four electronic parameters are used to explore the variation in energy with the amount of distortion from 0h symmetry. These are the energy difference between the xenon 5s and 5p orbitals, the spin‐orbit coupling constant for xenon 5p, and two Slater‐Condon electron repulsion parameters. Pure bending vibrational modes of t1u, t2g, and t2u symmetries are examined. The mixing of xenon 5s and 5p orbitals by the t1u vibration is particularly important, leading to a possible pseudo‐Jahn‐Teller distortion from 0h symmetry. Calculations of the vibrational force constants and frequencies are made for the bending modes, and the results are compared with observed values for other hexafluorides and related complexes. Calculations made on the coupling between t1u and t2g modes indicate an enhanced stabilization of the C3v structure. These studies lend support to the interpretation of the observed anomalous properties of the xenon hexafluoride molecule in terms of nonrigid octahedral structure but not to interpretations requiring thermally populated spin‐triplet excited states