The stable-carbon kinetic isotope effects of the reactions of isoprene, methacrolein, and methyl vinyl ketone with ozone in the gas phase

Abstract

The stable-carbon kinetic isotope effects (KIEs) for the gas-phase reactions of isoprene, methacrolein (MACR), and methyl vinyl ketone (MVK) with ozone were studied in a 25 L reaction chamber at (298 ± 2) K and ambient pressure. The time dependence of both the stable-carbon isotope ratios and the concentrations was determined using a gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) system. The volatile organic compounds (VOCs) used in the KIE experiments had natural-abundance isotopic composition thus KIE data obtained from these experiments can be directly applied to atmospheric studies of isoprene chemistry.

12C/13C kinetic isotope effects of the gas-phase reactions of isoprene, methacrolein, and methyl vinyl ketone with OH radicals

“…The average OH ε values for MACR and MVK are both lower than predicted from the N C -1 KIE dependence. This is similar to the findings reported by Iannone et al (2008) for the KIEs of the reaction of MVK and MACR with ozone. Iannone et al (2008) showed that an inverse dependence on molecular mass (MM) will also provide a useful approximation.…”

“…The gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) technique used in this investigation is very similar to those described previously for the measurements of stable carbon isotope KIE values (Anderson et al, 2004a(Anderson et al, ,b, 2007aIannone et al, 2003Iannone et al, , 2008. KIE experiments are similar in concept to relative rate (RR) experiments.…”

“…These KIE measurements complement the very recent analogous KIE study for these VOCs in reaction with ozone (Iannone et al, 2008). In both studies, measurements were made using VOCs without artificial enrichment or depletion of 13 C and thus their results are directly applicable to atmospheric reactions.…”

“…n-alkanes + OH, alkenes + O 3 , etc. ), KIE values were fitted as a function of the inverse carbon number, N C -1 Iannone et al, 2003Iannone et al, , 2008Anderson et al, 2004aAnderson et al, ,b, 2007a. As can be seen from Figure To date, there are no previously published KIE values for the reactions of MVK and MACR with OH radicals.…”

“…The application of 13 C/ 12 C studies toward determining the photochemical history of the studied VOC requires knowledge of the isotopic fractionations associated with its chemical removal processes . Several experimental studies have contributed toward the development of a database of 13 C/ 12 C kinetic isotope effect (KIE) values associated with key gas-phase reactions Iannone et al, 2003Iannone et al, , 2008Anderson et al, 2004aAnderson et al, ,b, 2007a. All of the previous studies employed gas-chromatography combustion isotope ratio mass spectrometry (GC-IRMS) instrumentation to analyze gas-phase reaction mixtures from Teflon chambers.…”