Vibrational spectrum and force field of molybdenum hexafluoride

Abstract

Infrared and Raman spectra are reported for 92MoF6 and 100MoF6 vapor (isotopic purities ≳ 97%). The infrared-active stretching fundamental ν3 exhibits partially resolved PQR structure with an asymmetric Q branch, from which the band origin ν0 can be estimated; the isotopic frequency shift for the band origin is Δν3 = 8.1±0.3 cm−1. The shift of the Q branch maximum of the other F1u fundamental is Δν4 = 3.0±0.4 cm−1. With the aid of these two isotope shifts, the general quadratic symmetry and valence force constants of MoF6 are calculated. The primary valence force constants are fr = 4.94 and fα ? 0.22 mdyn/Å. The force fields of MoF6, WF6, and UF6 are compared and discussed.