Combustion Research Facility, Sandia National Laboratories, 7011 East Avenue, MS 9055, Livermore, California 94551, USA.
Phys Chem Chem Phys. 2018 Jul 25;20(29):19373-19381. doi: 10.1039/c8cp03606c.
Methyl vinyl ketone (MVK) and methacrolein (MACR) are important intermediate products in atmospheric degradation of volatile organic compounds, especially of isoprene. This work investigates the reactions of the smallest Criegee intermediate, CH2OO, with its co-products from isoprene ozonolysis, MVK and MACR, using multiplexed photoionization mass spectrometry (MPIMS), with either tunable synchrotron radiation from the Advanced Light Source or Lyman-α (10.2 eV) radiation for photoionization. CH2OO was produced via pulsed laser photolysis of CH2I2 in the presence of excess O2. Time-resolved measurements of reactant disappearance and of product formation were performed to monitor reaction progress; first order rate coefficients were obtained from exponential fits to the CH2OO decays. The bimolecular reaction rate coefficients at 300 K and 4 Torr are k(CH2OO + MVK) = (5.0 ± 0.4) × 10-13 cm3 s-1 and k(CH2OO + MACR) = (4.4 ± 1.0) × 10-13 cm3 s-1, where the stated ±2σ uncertainties are statistical uncertainties. Adduct formation is observed for both reactions and is attributed to the formation of a secondary ozonides (1,2,4-trioxolanes), supported by master equation calculations of the kinetics and the agreement between measured and calculated adiabatic ionization energies. Kinetics measurements were also performed for a possible bimolecular CH2OO + CO reaction and for the reaction of CH2OO with CF3CHCH2 at 300 K and 4 Torr. For CH2OO + CO, no reaction is observed and an upper limit is determined: k(CH2OO + CO) < 2 × 10-16 cm3 s-1. For CH2OO + CF3CHCH2, an upper limit of k(CH2OO + CF3CHCH2) < 2 × 10-14 cm3 s-1 is obtained.
甲基乙烯基酮（MVK）和甲基丙烯醛（MACR）是挥发性有机化合物大气降解过程中重要的中间产物，特别是异戊二烯。本工作使用多路光电离质谱（MPIMS），分别用先进光源或莱曼-α（10.2eV）辐射可调谐同步辐射源作为光电离源，研究了最小的 Criegee 中间体 CH2OO 与其异戊二烯臭氧化产物 MVK 和 MACR 的反应。CH2OO 通过 CH2I2 的脉冲激光光解在过量 O2 的存在下产生。通过时间分辨测量反应物的消失和产物的形成来监测反应进程；通过 CH2OO 衰减的指数拟合获得一级反应速率常数。在 300K 和 4Torr 下，CH2OO 与 MVK 的双分子反应速率常数为 k(CH2OO + MVK) = (5.0 ± 0.4) × 10-13 cm3 s-1，CH2OO 与 MACR 的双分子反应速率常数为 k(CH2OO + MACR) = (4.4 ± 1.0) × 10-13 cm3 s-1，其中给出的 ±2σ 不确定度是统计不确定度。两种反应都观察到加合物的形成，这归因于形成次级臭氧化物（1,2,4-三恶烷），动力学的主方程计算和测量与计算的绝热电离能之间的一致性支持了这一结论。在 300K 和 4Torr 下，还对 CH2OO 与 CO 的可能双分子反应和 CH2OO 与 CF3CHCH2 的反应进行了动力学测量。对于 CH2OO + CO，未观察到反应，并确定了上限：k(CH2OO + CO) < 2 × 10-16 cm3 s-1。对于 CH2OO + CF3CHCH2，得到 k(CH2OO + CF3CHCH2) < 2 × 10-14 cm3 s-1 的上限。
