College of Physics and Electronics, Shandong Normal University, Jinan 250014, Shandong, China.
J Chem Phys. 2018 Jul 21;149(3):034302. doi: 10.1063/1.5037542.
The reaction of OH radicals with HBr plays a key role in atmospheric chemistry as the reaction, OH + HBr → Br + HO, produces Br atoms that destroy ozone. The experimental measurements of the kinetic isotope effect of k(OH + HBr)/k(OH + DBr) found that the kinetic isotope effects are temperature-independent. However, previous quasi-classical trajectory calculations on an accurate ab initio potential energy surface showed that the kinetic isotope effect is temperature-dependent. By contrast, the present full-dimensional time-dependent quantum dynamics calculations on the same potential energy surface find that the kinetic isotope effect is temperature-independent, agreeing well with the experimental studies both qualitatively and quantitatively. Furthermore, the rate constants from both quantum dynamics and quasi-classical trajectory calculations have a peak at around 15 K whereas the experimental data are not available in this low temperature range. The good agreement of the temperature-dependence of kinetic isotope effects between the present quantum dynamics calculations and the experimental measurements indicates that the kinetic isotope effect of k(OH + HBr)/k(OH + DBr) should be temperature-independent and the peak of the rate constants from the theoretical calculations call for experimental measurements at a very low temperature range.
OH 自由基与 HBr 的反应在大气化学中起着关键作用，因为该反应 OH + HBr → Br + HO 会产生破坏臭氧的 Br 原子。实验测量发现，OH + HBr/OH + DBr 的动力学同位素效应与温度无关。然而，先前在精确从头算势能表面上进行的准经典轨迹计算表明，动力学同位素效应与温度有关。相比之下，目前在相同势能表面上进行的全维时变量子动力学计算发现，动力学同位素效应与温度无关，与实验研究在定性和定量上都吻合得很好。此外，量子动力学和准经典轨迹计算的速率常数在 15 K 左右达到峰值，而实验数据在这个低温范围内不可用。本量子动力学计算与实验测量的动力学同位素效应的温度依赖性之间的良好一致性表明，OH + HBr/OH + DBr 的动力学同位素效应应该与温度无关，理论计算的速率常数峰值需要在非常低的温度范围内进行实验测量。
