Infrared and Raman Spectra of Polycrystalline Glyoxal

Abstract

The infrared spectrum from 4000 to 70 cm⁻¹ and the laser Raman spectrum of thin films of polycrystalline glyoxal at − 185°C are reported. A 400:1 N₂–glyoxal matrix frozen at 5°K helped to identify exciton components. There appears to be little difference in symmetry between the “free” and the crystallized or matrix isolated molecule which retains a centrosymmetric s‐trans structure in the crystal. The infrared bands originating from fundamental vibrations ${\nu }_{10}{\mathrm{,\; \nu }}_{11},\mathrm{and}{\nu }_{12}$ are each exciton split into three components while two of the Raman bands, ${\nu }_1$ and ${\nu }_4$ exhibit four components. These observations lead to the conclusion that each molecule occupies a $C_i$ site in the crystal, and the factor group or unit cell group of the crystal must be isomorphous with $D_{\text{2h}}$ .