Irikura Karl K, Francisco Joseph S
Physical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8380, USA.
J Phys Chem A. 2007 Jul 26;111(29):6852-9. doi: 10.1021/jp071314c. Epub 2007 Jun 20.
Sudden ozone depletion events in the marine boundary layer are associated with jumps in the CH3Br mixing ratio, but current models of atmospheric chemistry explain neither the ozone depletion nor the CH3Br spikes. We have used ab initio theory to predict the forward and reverse rate constants for the competing hydrogen abstraction and homolytic substitution (SH2) channels of the title reactions. Including the spin-orbit stabilization of the transition structures increases the rate constants by factors between 1.3 and 49. For the atmospherically relevant case of CH3I, our findings suggest that the hydrogen abstraction and homolytic substitution reactions are competitive. The predicted branching fraction to CH3Br is about 13%.
海洋边界层中的突发性臭氧消耗事件与CH₃Br混合比的跃升有关，但当前的大气化学模型既无法解释臭氧消耗现象，也无法解释CH₃Br峰值。我们利用从头算理论预测了标题反应中竞争性氢提取和均裂取代（SH2）通道的正向和反向速率常数。包括过渡结构的自旋轨道稳定化在内，速率常数增加了1.3至49倍。对于大气中相关的CH₃I情况，我们的研究结果表明氢提取和均裂取代反应具有竞争性。预测生成CH₃Br的分支比约为13%。
