Lattice and Molecular Vibrations in Single Crystal I2 at 77 K by Inelastic Neutron Scattering

Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 Å) and the other to represent the more distant interactions. Moderate agreement is obtained between the observed and calculated frequencies, but it also oappears necessary to treat the second-nearest-neighbor interaction (3.97 Å) separately from the van der Waals interactions (distances ⩾ 4.2 Å).