Abstract
The vibrational spectrum of gaseous oxalic acid was studied. Oxalic acid is a planar molecule with C[2h] symmetry and 18 fundamentals. Two structures based on electron diffraction studies have previously been proposed: [chemical diagram]. 8 infrared bands of gaseous oxalic acid were observed in the frequency range 4000 - 350 cm[-1]. 5 were assigned to inplane fundamental modes, 2 were assigned to out of plane fundamental modes, and only 1 was assigned to combination mode. 5 Raman bands of gaseous oxalic acid were observed and all were assigned to inplane fundamental modes. Previously 6 infrared bands have been observed but no previous Raman study of the vapour has been published. A Urey-Bradley force field (refined by trial and error) was used to calculate frequencies, potential energy distributions and normal modes of vibration for both structures. The spectroscopic assignments and vibrational analysis arc equally consistent with the two proposed structures and therefore support a centro-symmetric structure. The contours of the infrared bands do not help in assigning the fundamentals because the inplane bands are A-B hybrids. In addition the moments of inertia of both structures are too close to be able to decide between the two structures. The infrared spectra were recorded with a 60 cm path gas call and a Perkin-Elmer 457 spectrometer. Temperatures between 70°C and 125°C were used. The Raman spectra ware recorded with a Spex 1401 spectrometer and approximately 2 watts at 5145A from a Spectra-Physics 164 laser. Temperatures between 140°C and 185°C were used.