Vibrational Analysis of the Infrared and Raman Spectra of Oxalyl Bromide in the Crystalline and Fluid States

• Published in: The Journal of chemical physics 1971-01, Vol.54 (6), p.2367-2374
• Main Authors: Durig, J. R., Hannum, S. E., Baglin, F. G.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1675188

The vibrational spectrum of oxalyl bromide [COBr]2, has been recorded between 4000 and 33 cm−1. The infrared spectra of oxalyl bromide have been examined in the solid, liquid, and gaseous states, and the Raman spectra of the solid and liquid have been observed and qualitative depolarization ratios have been measured. The vibrational spectrum of the crystalline material has been interpreted on the basis of C2h molecular symmetry and C2h5 space group symmetry. Two of the three external lattice modes have been observed in the far-infrared spectrum, and at least four of the six Raman active external lattice modes have also been observed. Six bands appear in the infrared and Raman spectra of the liquid/gaseous states which do not appear in the spectra of the solid. Thus, in the fluid states, molecules with both C2h and C2υ molecular symmetries appear to be present. The enthalpy difference between the two isomers was determined by a variable temperature study to be 2.9 ± 0.1 kcal/mol with the trans isomer being more stable. A rough estimate of the equilibrium mixture at room temperature gives a value of 10% ± 5% for the cis isomer. The barrier restricting the internal rotation around the C–C single bond appears to be governed mainly by V1 and V2 terms of approximately the same order and in the range of 3 kcal/mol.