DIRECTIONS OF VIBRATIONAL TRANSITION MOMENTS IN A MOLECULAR CRYSTAL OF LOW SYMMETRY.
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Date
1961
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Ohio State University
Abstract
The absorption of eleven infra-red active in-plane modes of crystalline monoclinic adipic acid was investigated as a function of the angle between the electric vector of linearly polarized incident radiation and the crystallographic \emph{c} axis in order to gain information concerning relationships between frequency dependent dielectric axes, directions of transition moment vectors, and chemical structure in a molecular crystal with low symmetry. The frequently used approximation which assumes that absorbance is proportional to the squared dot product of the electric vector and the transition vector can lead to serious errors. Transition moment directions were therefore calculated by taking into account frequency dependent dielectric properties of the crystal. The results were compared with hypothetical idealized directions based on bond structure and local symmetry. The polarization of some modes which are commonly referred to as separable and characteristic was not in agreement with simple prediction. Some factors influencing directions of transition moments in systems of low symmetry are briefly discussed.
Description
$^{*}$Eastern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.
Author Institution: Eastern Regional Laboratory,^{*}
Author Institution: Eastern Regional Laboratory,^{*}