Model stretching overtone eigenvalues for SF6, WF6, and UF6

Abstract

A four parameter potential model for the stretching modes of XY₆ octahedra is shown to give an excellent fit to the published experimental vibrational eigenvalues of SF₆, WF₆, and UF₆. A new technique for the automatic computation of symmetrized local mode basis functions is used to generate eigenvalues, converged to within 1 cm⁻¹, for overtone and combination states up to v_tot=v₁+v₂+v₃=6 for WF₆ and UF₆. Similar convergence for SF₆ is possible only up to v_tot=4 due to axial momentum transfer arising from the relatively low central mass, which renders a local mode basis less convenient for this molecule. The most striking result for both WF₆ and UF₆ is that the highest component of the nν₃ manifold for n≤6 appears to lie within 1 cm⁻¹ of n multiples of the ν₃ fundamental. The continuation of such a pattern up to dissociation would imply that no special anharmonic resonances are needed to account for the infrared multiphoton dissociation.