Vibrational Spectroscopic Investigation of Molecular Crystals of Methylmercury(II) Halides

A nearly full assignment of the vibrational modes of methylmercury halide crystals has been proposed. Factor group analysis has been used to derive the vibrational selection rules for the lattice modes. It is concluded that the D2hU structure with four molecules in the unit cell. Lattice modes for CH.-sHgl and CD.-jHgl can be assigned on the basis of C2hU substructure with two molecules per unit cell. The bromide gave an ultra-low wavenumber band (7.0 cm-1) which we were unable to assign. Force constants have been calculated on the basis of a primitive unit cell (containig two molecules). The internal HgX stretching force constants 2.112, 1.658, 1.507 and 1.347 N cm-1 and the transverse translatory force constants 0.719, 0.364, 0.266 and 0.218 N cm-1 obtained for fluoride, chloride, bromide, and iodide, respectively, show strong dependence on the kind of halide