Optic-type vibrational modes of liquid chalcogens

We carried out inelastic neutron scattering (INS) measurements to study the dynamic structure of liquid (l-) Se and Te₅₀Se₅₀. The bond-stretching modes for both liquids were found to lie in higher energies than those forming a trigonal phase, showing that the chainlike molecules are more isolated than in the trigonal phase. The Q-dependence of the intensity of the dynamic structure factor was examined at the region of the stretching modes, and found to be explained by a simple model where we assumed completely out-of-phase motions of two atoms. The result shows the possibilities of extracting short-range structural information from such Q-dependences for these kinds of basically isolated molecules.