SELECTION RULES FOR FUNDAMENTAL MODES OF CHAIN MOLECULES
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Date
1954
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Ohio State University
Abstract
The symmetry of an aligned chain molecule is characterized by a ""line"" group, a one-dimensional space group. The selection rules for such a molecule are determined by the factor group of the line group. The number of normal modes in each symmetry class is determined by the atoms contained in a single repeat unit. In a crystal, the site group of a chain molecule is a line group rather than a point group. The selection rules are determined by the factor group of the site group. The selection rules under the space group are derived in the same way as for a molecular crystal, considering only those atoms contained in a single unit cell. Some of the lattice modes are, however, classified as internal modes. The connection between the site and space groups for polymer chain crystals and those for ordinary molecular crystals is pointed out, and a possible application to hydrogen bonding indicated. These ideas are illustrated in detail for polyethylene.
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Author Institution: Olin Industries