Reactions of atmospheric peroxy radicals studied by synchrotron VUV multiplexed photoionization mass spectrometry

Abstract

Peroxy radicals are key intermediates in the oxidn. chem. of both anthropogenic and biogenic Volatile Org. Compds.(VOCs) in the troposphere. These species are central in the formation of photochem. smog and org. aerosols, and can be formed from abstraction reactions or from addn. reactions with unsatd. hydrocarbons. Lab. studies of the kinetics of peroxy radical reactions are complicated by the many competing self- and cross-reactions that typically occur. The large no. of possible products, esp. chain-propagating radical channels, further complicates the chem. Here we describe recent expts. using time-resolved photoionization mass spectrometry (PIMS) with ionization by VUV synchrotron radiation. This method provides a powerful, highly sensitive technique for studying the product branching ratios and reaction rates, by selective time-resolved detection of many of the reactants, intermediates, and primary products. We report investigations of peroxy radical reactions in a laser-photolysis low-pressure flow cell expt. that utilizes tunable VUV radiation generated at the Advanced Light Source synchrotron at the Lawrence Berkeley Lab., coupled to the Sandia multiplexed PIMS app. We have performed expts. on the reactions of the acetyl peroxy radicals, as well as the selfreaction of the Et peroxy radical. We are able to det. relative product yields based on measurements of abs. radical concns., new abs. photoionization cross sections, with the aid of kinetic modeling.