The infrared spectrum and molecular structure of gaseous UF4

The infrared spectrum of gaseous UF4 was measured in the range of 75-700 cm(-1). Absorptions found at 537 and 114 cm(-1) were the asymmetric stretching frequency nu(3) and the deformation frequency nu(4) respectively. In addition, a re-analysis of previously published gas electron diffraction data has been made, testing four geometric models for the UF4 molecule (T-d, C-3v, C-2v and D-2d symmetry), The spectroscopic and electron diffraction data are compatible with a tetrahedral symmetry for the UF4 molecule. The bond distance r(alpha) (U-F) is 201.7(5) pm. By means of joint analysis of the electron diffraction and spectroscopic data, the symmetric stretching frequency was estimated to be nu(2) = 123 cm(-1) Coriolis constants were calculated using the Delta nu(PR) value of the nu(3) band. The molecular parameters of tetrahedral UF4 were used for the calculation of the entropy S degrees(1050 K, UF4, g) = 492.8 +/- 3.0 J mol(-1) K-1.