Vol. 13, issue 02, article # 1

Abstract:

IR absorption spectra of XF₃ and XF₅ (X = Cl and Br) molecules in gas phase and cryogenic solutions of Kr (T = 130 K) and Xe (T = 180 K) within wide range of frequencies (200-2500 cm^-1) including the range of the 3rd order transitions were studied. Integral value of the absorption coefficient of the ν₇(E) band of XF₅ has been determined, as well as relative intensities of all bands observed in the XF₅ infrared spectrum and anharmonicity constants for some XF₃ and XF₅ vibrations. It is shown that contrary to BrF₃, a splitting of asymmetrical vibration band into (Cl-F)ax bonds of ClF₃ is due to Coriolis interaction between energetically close levels ν₁(A₁) and ν₄(B₁) when the molecule rotates about the axis of maximum moment of inertia. Based on analysis of spectroscopic data, results of ab initio calculations, as well as estimates of the polarization d-functions importance for central atom and effects of electron correlation, the conclusion was drown that the model for calculating the infrared intensities for XF₅ (X = Cl and Br) molecules should take into account both the difference in characters of (X-F)_ax and (X-F)_eq bonds and contributions from nonrigid intramolecular regroupings according to tourniquet mechanism.