Journal of Molecular Spectroscopy, Volume 21, Issue 1-4, p. 48-65.

The infrared spectra of dimethyl oxalate in the vapor, liquid and crystalline phases and as a solution in CCl₄ or CS₂ have been recorded from 2-35 μ together with the Raman spectrum of the liquid. Both the spectral data and dipole moment evidence support a nonplanar species having point symmetry C₂ in the liquid and vapor phases, the carboxylate groups deviating from a planar cis configuration by ~20° and being rotated about the C-C bond by ~+/-40° relative to the trans configuration. A complete assignment, with the exception of the torsional modes, has been made of the liquid and vapor spectra on the basis of this species, while the spectrum of the crystalline solid has been assigned assuming a planar trans species having point symmetry C_2h.