Vapour-phase intensity studies of the Raman-active bands of Group 6 hexafluorides

Abstract

The vapour-phase Raman spectra of sulphur(VI), selenium(VI), and tellurium(VI) fluorides have been recorded with 488.0- and/or 514.5-nm excitation at ca. 0.5 atm and ca. 295 K. The intensities of the ν₁(a_1g), ν₂(e_g), and ν₅(t_2g) bands have been determined relative to that of the ν₁(a₁) band of methane as external standard, and this has permitted the calculation of Raman scattering activities and differential cross sections for each band. Molecular-(′_j), bond-(′_MX), and bond-component (α′‖, α′⊥) polarisability derivatives, as well as bond anisotropies (γ_MX), have been deduced in all cases. The ′_MF values are in the order ′_SeF(1.73) > ′_TeF(1.65) > ′_SF(1.35 Ų), which agrees with the predictions of a delta-function potential model of chemical bonding and hence with fractional Pauling covalent bond characters of SF (0.61) SeF (0.60) TeF (0.47). A Pauling electronegativity for tellurium of 2.25 is deduced on the basis of the model.