RAMAN SPECTRA OF SOLID CHLORINE AND BROMINE

Librational lattice modes have been observed at 15°K in solid Cl 2 at 83, 100, and 118 cm-1, and at 55, 74, 86, and 101 cm-1 in solid Br2. Their intensities relative to one another can be qualitatively accounted for by the oriented gas model. The stretching frequencies [ν(1-0)] of Cl2 and Br2 are shifted -13 and - 20 cm-1, respectively, from their gas phase values and show structure due to isotope splittings and intermolecular coupling. The spectra of the lattice modes, the Br2 stretching motion, and the Cl2 stretching motion indicate, respectively, strong, intermediate, and weak intermolecular coupling relative to the isotope splittings. Both lattice and internal frequencies indicate stronger intermolecular forces in solid Br2 than in solid Cl2.