Atmospheric chemistry of the HC(O)CO radical

The chemistry of the HC(O)CO radical, produced in the oxidation of glyoxal, has been studied under conditions relevant to the lower atmosphere using an environmental chamber/Fourier Transform infrared spectrometric system. The chemistry of HC(O)CO was studied over the range 224-317 K at 700 Torr total pressure and was found to be governed by competition between unimolecular decomposition [to HCO and CO, reaction (5)] and reaction with O₂ [to form HO₂ and 2CO, reaction (6a), or HC(O)C(O)O₂, reaction (6b)]. The rate coefficient for decomposition relative to that of reaction with O₂ increases with increasing temperature. Assuming a value for k₆ of 10^-11 cm³ molecule^-1 s^-1, the following expression for the unimolecular decomposition is obtained at 700 Torr, k₅ = 1.4⁺⁹/_-1.1×10¹²exp(-3160±500/T). The rate coefficients for reactions (6a) and (6b) are about equal, with no strong dependence on temperature. The reaction of HC(O)C(O)O₂ with NO₂ was also studied. Final product analysis was consistent with the formation of HCO, CO₂, and NO₃ as the major products in this reaction; no evidence for the PAN-type species, HC(O)C(O)O₂NO₂, was found even at the lowest temperature studied (224 K). The UV-visible absorption spectrum of glyoxal is also reported; results are in substantive agreement with previous studies.