The Stable-carbon Kinetic Isotope Effects Of The Reactions Of Isoprene, Methacrolein, And Methyl Vinyl Ketone With Ozone In The Gas Phase

摘要

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 chroma-tography 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. All ~(13)C/~(12)C KIEs reported herein are as per mille ε values, where ε = (KIE - 1) × 1000'‰, and KIE = k_(12)/k_(13)- The following average stable-carbon KIEs were obtained: (8.40 ± 0.11 )‰ (isoprene), (8.38 ±0.42)‰ (MACR), and (8.01 ± 0.07)‰ (MVK). The stable-carbon KIE values of three 1-alkenes, which were used as reference compounds for relative rate experiments, were also determined: (5.48 ± 0.09)‰ (1 -heptene), (4.67 ± 0.17)‰ (1 -octene), and (4.59 ± 0.56)‰ (1 -nonene). The ε values for the reactions of isoprene and 1-heptene with ozone agree with measurements in a previous study [Iannone, R., Anderson, R.S., Rudolph, J., Huang, L., Ernst, D., 2003. The carbon kinetic isotope effects of ozone-alkene reactions in the gas-phase and the impact of ozone reactions on the stable carbon isotope ratio of alkenes in the atmosphere. Geophysical Research Letters 30, 1684, doi: 10.1029/2003GL017221.], but the values presented here have a substantially improved accuracy. The e values for 1-octene and 1-nonene reactions with ozone have not been measured before and closely follow the 1/N_C dependence (where N_c represents the number of carbon atoms in the alkene) derived in the aforementioned study. MACR and MVK had ε values that were somewhat below the expected range of values predicted by the 1/N_c dependence found for alkenes.