LASER RAMAN-SPECTROSCOPY OF SOME URANYL TRINITRATE COMPLEXES (MUO(2)(NO3)(3) M=CS, RB, K, NH4)

The laser Raman spectra of four uranyl trinitrate complexes (MUO(2)(NO3)(3); M = Cs, Rb, K, NH4) are recorded in the region from 2000 to 10 cm(-1) by using the lambda = 514.5 (Ar+), 528.7 (Ar+), and 632.8 nm (He-Ne) laser excitation lines. Their vibrational assignments are made on the assumption that all the complexes contain discrete UO(2)X(3)(-)(X = NO3) ions belong to a point group of D-3h. In order to support such assignments, normal coordinate analyses of the skeletal vibrations are carried out on the basis of a modified valence force field including the bond-bond angle-angle interactions. Approximate stretching and bending force constants of the U-O and U-X bonds in the UO(2)X(3)(-), anion are obtained with additional force constants of opposite U-O bond-bond, adjacent U-X bond-bond and angle-angle interactions. Apart from lambda = 632.8 nm, for lambda = 514.5 and 528.7 nm, the resonance Raman scattering is observed for each complex. It is found that, as resonance is approached, the uranyl symmetric stretching vibration at c. 880 cm(-1) is conspicuously enhanced in comparison with the NO3- vibration at c. 1025 cm(-1).