Matrix Isolation and ab Initio Studies of Oxalic Acid

Article abstract of DOI:10.1021/j100192a024

Rotamerization and UV photochemical decomposition of oxalic acid were studied in solid Ne, Ar, and Xe matrices.The energies and spectra of the conformers and photoproducts were also stimulated by extensive ab initio calculations at MP2/6-31G** (energies, geometries) and MP2/4-31G* (numerical frequencies) levels.Two conformers were found to be present in matrices, the lowest energy species being cTc (with two intramolecular hydrogen bonds) and species cTt (with only one intramolecular hydrogen bond) being at ca. 7 kJ mol^-1 higher in energy.The uphill process cTc -> cTt could be initiated by UV excitation at wavelengths of ca. 270 nm.IR irradiation at wavenumbers above 2000 cm^-1 was found to promote the reverse interconversion.Full Xe are irradiation decomposes oxalic acid in matrices, the product yield ratio being different in different hosts.On the basis of ab initio calculations, the possible transition states for photon shifts are discussed.The calculated vibrational spectra are given for six conformers of oxalic acid, the spectra of the observed conformers are assigned, and their potential energy distributions are given.