Infrared spectroscopy of fluoride molecules in noble gas solutions

Abstract

Infrared spectra of the spherical top molecules XF₆ (X = S, U, Mo, W) dissolved in liquefied argon, krypton and xenon have been studied. It is shown that the observed Lorentz shape of the bands results from two processes: vibrational dephasing and rotational diffusion. In contrast to fundamental transitions A_1g - F_1u, for the (v ₂ + v ₃) state it has proved necessary to apply two limiting cases: when the anharmonic level splitting ΔE _anh is much greater than the Coriolis coupling, and when ΔE _anh is small relative to the Coriolis coupling. Measured values of band halfwidths are compared with the theoretical values, obtained with the help of a rotational diffusion model. It is concluded that, in contrast to SF₆, vibrational dephasing and intermolecular interactions contribute essentially to the formation of band contours of heavy metal hexafluorides. The second moment for the (v ₂ + v ₃) band has been estimated. The characteristic times of angular momentum correlation for SF₆, UF₆, MoF₆ and WF₆ molecules in cryosolutions have been calculated. The measured values of vibrational band shifts and anharmonicity constants for XF₆ molecules due to intermolecular forces in ‘gas-cryosolution’ transition have been compared with consequent theoretical estimations.