The Gas-Phase Photochemistry of Oxalic Acid

Article abstract of DOI:10.1021/j100250a014

The photolysis of oxalic acid has been studied in the gas phase at wavelengths from 257 to 313 nm, corresponding to excitation of the <*>(¹A_u,?^*<-n₊) first excited singlet state.Products were CO2, CO, H2O, and HCOOH, all formed linearly with time and with product ratios independent of wavelength and added gases.It is concluded that two primary processes occur, yielding CO2 + HCOOH and CO2 + CO + H2O, respectively, with the yield of the first about 2.6 times that of the second.Weak fluorescence has been observed accompanying the photolysis.The mercury (³P₁)-photosensitized decomposition was also studied and was very similar to the direct photolysis, after correcting for secondary decomposition of formic acid.The infrared multiphoton decomposition of oxalic acid vapor was also briefly examined by using a pulsed CO2 laser operating at 935 cm^-1.The same two processes were observed, but with yields of CO approaching those of CO2 and the second process thus more important than the first.Mechanisms in the three systems are discussed.It is suggested that the ultraviolet photolysis may proceed through the dihydroxymethylene radical, formed directly from the excited state, while the infrared multiphoton decomposition probably involves a simple decomposition of the vibrationally excited ground state.