LATTICE AND MOLECULAR VIBRATIONS IN IODINE
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Date
1973
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Ohio State University
Abstract
There is considerable scientific effort expended in determining intermolecular potential functions in cyrstals. Inelastic neutron scattering is a powerful technique for studying intermolecular forces; however, phonon dispersion curves have been obtained for only a few molecular crystals at this time and much work remains to be done in this field. The dynamics of the halogen crystals are of particular interest since there is good reason to believe the intermolecular interactions are important, and yet the systems are probably simple enough to make a first-principles analysis of the dispersion curves. Iodine is particularly important since it is a solid at room temperature and crystals can be more readily obtained than for the other halogens. In addition, iodine is known to complex with a large number of compounds, as well as with itself. A knowledge of the lattice dynamics of iodine should give some insight into the nature of these intermolecular interactions. Phonon dispersion curves have recently been measured at $77^{\circ} K$ at the HFIR in the [001], [010], and [0, $\epsilon$,.5] directions with polarization vectors in the yz-plane. All the branches were identifiable except in the [010] direction where there may be considerable overlap and mixing of the optical and librational modes. The internal symmetric and asymmetric stretching modes at q = 0 are in good agreement with a polycrystalline Raman study but at variance with an infra-red study. The dispersion of these two modes in the [001] direction was readily observable with the aid of intensity considerations. Measurements are to be made in other symmetry directions and for those branches perpendicular to the molecular plane.
Description
M. Nielsen is a guest scientist from Atomic Energy Research Establishment Ris\""{o}, Roskilde, Denmark. The Oak Ridge National Laboratory is operated by Union Carbide Corporation for the USAEC. THE FOLLOWING PAPERS ($\Delta$1-$\Delta$8) WERE RECEIVED LATER THAN THE ONES IN THE $\Sigma$ SESSIONS:
Author Institution: Solid State Division, Oak Ridge National Laboratory
Author Institution: Solid State Division, Oak Ridge National Laboratory