Direct kinetics study of CHzOO + methyl vinylketone and CH20 0 + methacrolein reactions andan upper limit determination for CH20 0 + COreaction

摘要

Methyl vinyl ketone (MVK) and methacrolein (MACR) are important intermediate products in atmosphericdegradation of volatile organic compounds, especially of isoprene. This work investigates the reactions ofthe smallest Criegee intermediate, CH20 0 , with its co-products from isoprene ozonolysis, MVK andMACR, using multiplexed photoionization mass spectrometry (MPIMS), with either tunable synchrotronradiation from the Advanced Light Source or Lyman-a (10.2 eV) radiation for photoionization. CH20 0 wasproduced via pulsed laser photolysis of CH2l2 in the presence of excess 0 2. Time-resolved measurementsof reactant disappearance and of product formation were performed to monitor reaction progress; firstorder rate coefficients were obtained from exponential fits to the CH20 0 decays. The bimolecularreaction rate coefficients at 300 K and 4 Torr are /c(CH2〇〇 + MVK) = (5.0 ± 0.4) x 10-13 cm3 s-1 and/c(CH2〇〇 + MACR) = (4.4 ± 1.0) x 10—13 cm3 s_1, where the stated ±2a uncertainties are statisticaluncertainties. Adduct formation is observed for both reactions and is attributed to the formation of asecondary ozonides (1,2,4-trioxolanes), supported by master equation calculations of the kinetics and theagreement between measured and calculated adiabatic ionization energies. Kinetics measurementswere also performed for a possible bimolecular CH20 0 + CO reaction and for the reaction of CH20 0with CF3CHCH2 at 300 K and 4 Torr. For CH20 0 + CO, no reaction is observed and an upper limitis determined: /c(CH20 0 + CO) < 2 x 10-16 cm3 s- 1 For CH2〇〇 + CF3CHCH2, an upper limit ofk[CH2QO + CF3CHCH2) < 2 x 10~14 cm3 s- 1 is obtained.