单分子水对H_2O_2+Cl气相反应影响的理论研究

在aug-cc-pVTZ基组下采用CCSD(T)和B3LYP方法,研究了H2O2+Cl反应,并考虑在大气中单个水分子对该反应的影响.结果表明,H2O2+Cl反应只存在一条生成产物为HO2+HCl的通道,其表观活化能为10.21kJ·mol-1.加入一分子水后,H2O2+Cl反应的产物并没有发生改变,但是所得势能面却比裸反应复杂得多,经历了RW1、RW2和RW3三条通道.水分子在通道RW1和RW2中对产物生成能垒的降低起显著的负催化作用,而在通道RW3中则起明显的正催化作用.利用经典过渡态理论(TST)并结合Wigner矫正模型计算了216.7-298.2 K温度范围内标题反应的速率常数.结果显示,298.2 K时通道R1的速率常数为1.60×10-13cm3·molecule-1·s-1,与所测实验值非常接近.此外,尽管通道RW3的速率常数kRW3比对应裸反应的速率常数kR1大了46.6-131倍,但该通道的有效速率常数k'RW3却比kR1小了10-14个数量级,表明在实际大气环境中水分子对H2O2+Cl反应几乎没有影响.

Theoretical Study on the effect of a Single Water Molecule on the H2O2+Cl Gas Reaction

The reaction mechanism and rate constant of the H₂O₂+Cl reaction, with and without a single water molecule, was investigated theoretically at the CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory. The calculated results show that there is only one channel for the formation of HO₂+HCl in the naked H₂O₂+Cl reaction with an apparent activation energy of 10.21 kJ·mol^-1. When one water molecule is added, the product of the reaction does not change, but the potential energy surface of the reaction becomes complex, yielding three different channels RW1, RW2, and RW3. The single water molecule in the RW1 and RW2 reaction channels has a negative influence on reducing the reaction barrier for the formation of HO₂+HCl, whereas it has a positive influence in Channel RW3. Additionally, to estimate the importance of these processes in the atmosphere, their rate constants were evaluated using conventional transition state theory with the Wigner tunneling correction. The result shows that the rate constant for the naked H₂O₂+Cl reaction is 1.60×10^-13 cm³ ·molecule^-1 ·s^-1 at 298.2 K, which is in good agreement with experimental values. Although the rate constant of channel RW3 is predicted to be 46.6-131 times larger than that of the naked H₂O₂+Cl reaction, its effective rate constant is smaller by 10-14 orders of magnitude than that of the naked reaction, that is, for the H₂O₂ + Cl reaction the naked reaction almost exclusively occurs under tropospheric conditions.