最簡單克里奇中間體與水蒸氣反應之動力學同位素效應

Abstract

此實驗在壓力300 Torr和600 Torr以及溫度為298.9 K下以紫外線吸收光譜法測量最簡單克里奇中間體(CH2OO)與水蒸氣反應之動力學同位素效應(kinetic isotope effect, KIE, kH/kD)，另外還有觀察到CH2OO + 3H2O的反應途徑。此實驗結果給出未解析反應級數之KIE = 1.6 ± 0.2，若分成不同反應途徑作分析KIE會得到KIE(k1) = 1.47 ± 0.68、KIE(k2) = 2.23 ± 0.57和KIE(k3) = 1.01 ± 0.16。(CH2OO + n(H2O), kn)。KIE(k1)和KIE(k2)符合理論計算文獻的結果[DOI: 10.1039/C8CP02064G]，主要是由於氘化之後零點修正障壁能量較高造成此KIE數值，氫原子穿隧的貢獻很小；然而其並未計算KIE(k3)。由於此實驗提高了水濃度之精確度因此觀察到CH2OO與水蒸氣反應有微小的壓力效應，反應速率常數比k600torr/k300torr約為1.06 ± 0.04。

In this work, we measured the kinetic isotope effect (KIE = kH/kD) of the reaction between the simplest Criegee intermediate (CH2OO) and water vapor using UV absorption spectroscopy at pressures of 300 Torr and 600 Torr and temperatures of 298.9 K. Additionally, we observed a distinct reaction pathway of CH2OO + 3H2O. The results yield a reaction-order-unresolved KIE of 1.6 ± 0.2. When analyzing KIEs separately for different reaction pathways, we obtained KIE(k1) = 1.47 ± 0.68, KIE(k2) = 2.23 ± 0.57, and KIE(k3) = 1.01 ± 0.16 for (CH2OO + n(H2O), kn). The KIE(k1) and KIE(k2) results are consistent with those reported in a theoretical paper, [DOI: 10.1039/C8CP02064G] primarily attributed to the higher zero point corrected barrier energy upon deuteration, with a minimal contribution from hydrogen atom tunneling. However, KIE(k3) was not calculated in that paper. By improving the precision of water vapor concentration in our experiment, we observed a minor pressure effect in the reaction between CH2OO and water vapor, with the ratio of reaction rate constants k600torr/k300torr being approximately 1.06 ± 0.04.