INFRARED-SPECTROSCOPY OF FLUORIDE MOLECULES IN NOBLE-GAS SOLUTIONS .1. OCTAHEDRAL MOLECULES

Infrared spectra of the spherical top molecules XF(6) O(= 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 tw o processes: vibrational dephasing and rotational diffusion, In contra st to fundamental transitions A(1g)-F-1u, for the (nu(2) + nu(3)) stat e it has proved necessary to apply two limiting cases: when the anharm onic level splitting Delta E(anh) is much greater than the Coriolis co upling, and when Delta E(anh) is small relative to the Coriolis coupli ng. Measured values of band halfwidths are compared with the theoretic al values, obtained with the help of a rotational diffusion model. It is concluded that, in contrast to SF6, vibrational dephasing and inter molecular interactions contribute essentially to the formation of band contours of heavy metal hexafluorides. The second moment for the (nu( 2) + nu(3)) band has been estimated. The characteristic times of angul ar momentum correlation for SF6, UF6, MoF6 and WF6 molecules in cryoso lutions have been calculated. The measured values of vibrational band shifts and anharmonicity constants for XF(6) molecules due to intermol ecular forces in 'gas-cryosolution' transition have been compared with consequent theoretical estimations.