THE INFRARED-SPECTRUM AND MOLECULAR-STRUCTURE OF GASEOUS UF4

The infrared spectrum of gaseous UF4 was measured in the range of 75-7 00 cm(-1). Absorptions found at 537 and 114 cm(-1) were the asymmetric stretching frequency nu(3) and the deformation frequency nu(4) respec tively. In addition, a re-analysis of previously published gas electro n diffraction data has been made, testing four geometric models for th e UF4 molecule (T-d, C-3v, C-2v and D-2d symmetry), The spectroscopic and electron diffraction data are compatible with a tetrahedral symmet ry 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 spectro scopic 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.