Branching ratios and rate coefficients for the reaction of chlorine atoms with butanal, pentanal, methyl vinyl ketone and methacrolein

The photochemical oxidation of organic pollutants in the atmosphere occurs via a complex series of reactions involving oxides of nitrogen (NOx = NO + NO2), ozone, hydroxyl radicals, and peroxy radicals. The reaction between organic peroxy radicals (RO2) and hydroperoxy radicals (HO2) is important in this process, especially when levels of NOx are low. In order to study the reactions between HO2 and RO2 in the lab, it is necessary to first generate these radicals. Generation of the RO2 radial is most conveniently accomplished by photolyzing a mixture of aldehyde or ketone precursor and chlorine gas in the presence of oxygen.

The branching ratios and rate coefficients for the reaction of chlorine radicals with butanal, pentanal, methyl vinyl ketone, and methacrolein were investigated in a 142 L Teflon-lined reaction cell coupled with a Fourier transform infrared (FTIR) spectrometer. The rate coefficients were determined with the relative rate technique using ethene and isopropanol as tracers. The branching ratios were determined by measuring the yields of reaction products in the absence oxygen or in the presence of NOx. The implications of these results for HO2 + RO2 chemistry will be discussed.