Infrared and Raman Spectra of Substituted Hydrazines. III Symmetrical Dimethylhydrazine

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Abstract
The infrared spectra of gaseous, liquid, and polycrystalline symmetrical dimethylhydrazine and its deuterium analogs have been recorded from 70–4000 cm−1. The Raman spectra of the liquid and solid samples have also been recorded and depolarization values have been measured. A comparison of the infrared and Raman spectra of the respective compounds indicates that the liquid phase consists of approximately a 69:31% mixture of gauche conformers. An assignment of the observed frequencies based on band positions, relative intensities, and isotopic shifts is presented for both molecular conformations. Although the torsional fundamentals were observed for the molecules in both the gaseous and crystalline states, the bands observed for the solids were more clearly defined and were thus employed for the barrier height calculations. The threefold methyl rotational barrier is calculated to be approximately 3.3 kcal/mole, whereas the magnitude of the barrier hindering internal rotation about the N–N bond is estimated to be 5.0 kcal/mole.