PHONON SPECTRA OF THE PARTIALLY-DEUTERATED AND HEAVILY-DOPED, ISOTOP1C MIXED ETHYLENE CRYSTALS: THE SIMPLE AND GENERALIZED VIRTUAL CRYSTAL APPROXIMATION DISTINGUISHED
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Date
1978
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Ohio State University
Abstract
The Raman lattice modes of the partially-deuterated $ethylenes^{1}$ and of heavily-doped, isotopic mixed molecular crystals $C_{2}H_{4} :C_{2}D_{4} $ (25:75, 50:50 and 75:25) have been obtained. The spectra observed serve to distinguish the ``generalized”$^{2}$ and ``simple”$^{3}$ virtual crystal approximations. The effective masses of these systems (i.e. $C_{2}H_{3}D/75\%C_{2}H_{4}: 25\%C_{2}D_{4}, C_{2}H_{2}D_{2}/ 50\%C_{2}H_{4}: 50\%C_{2}D_{4}$, and $C_{2}HD_{3}/25\%C_{2}H_{4}: 75\%C_{2}D_{4})$ are the same; however, the distribution of the protons and deuterons, and thus the disorder, differs between the partially-deuterated systems end the mixed crystal systems. The difference in disorder would be undetectable if the systems could be described with the simple or isolated-band VCA; however, mixing occurs among librations originating from orthogonal molecular rotations in $ethylene,^{4,5}$ so the simple VCA may not apply in this case. A unique result of the generalized VCA is the dependence of the relative intensities on the disorder, which accounts for the differences in the relative intensities of the observed lattice modes for the partially-deuterated and mixed-crystal ethylene systems.
Description
$^{1}$R. G. Whitfield and G. E. Leroi, J. Chem, Phys., in press. $^{2}$H. K. Houg and R, Kopelman, J. Chem, Phys. 58, 384 (1973). $^{3}$J. C. Bellows and P. N. Prasad, J. Chem. Phys. 66, 625 (1977). $^{4}$G. R. Elliott and G. E. Leroi, J. Chem, phys. 59, 1217 (1973). $^{5}$R. G. Whitfield, Ph.D. thesis, Michigan State University, 1977.""
Author Institution: Department of Chemistry, Michigan State University Olin Chemicals Group
Author Institution: Department of Chemistry, Michigan State University Olin Chemicals Group