Xu Kun, Xu Zhen-Feng, Lin M C
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Phys Chem A. 2006 Jun 1;110(21):6718-23. doi: 10.1021/jp056241g.
The radical reaction mechanism of FCO + NO on the ground electronic state energy surface has been studied at the G2M level of theory based on the geometric parameters optimized at the B3LYP/6-311+G(d) level of theory. The two kinds of reaction pathways include the direct fluorine abstraction channel producing CO + FNO and the association channel forming the FC(O)NO complex. The former has a distinct barrier of 8.9 kcal mol(-1), while the latter is a barrierless association process. The rate constant of this reaction system in the temperature range 200-3000 K has been calculated by the microcanonical VTST/RRKM theory. The theoretical result shows that the predicted total rate constants exhibit a negative-temperature dependence and positive-pressure effect at lower temperatures. Under the experimental conditions, the predicted values are in good agreement with the experimental results. In addition, the predicted branching ratios clearly indicate that the dominant product channel is the formation of FC(O)NO at low temperatures and FNO + CO at high temperatures (>500 K).
基于在B3LYP/6-311+G(d)理论水平上优化的几何参数，在G2M理论水平下研究了FCO与NO在基态电子能面上的自由基反应机理。两种反应途径包括生成CO + FNO的直接氟提取通道和形成FC(O)NO络合物的缔合通道。前者有一个明显的8.9 kcal mol(-1)的势垒，而后者是一个无势垒的缔合过程。通过微正则变分过渡态理论/ Rice-Ramsperger-Kassel-Marcus (VTST/RRKM)理论计算了该反应体系在200-3000 K温度范围内的速率常数。理论结果表明，预测的总速率常数在较低温度下呈现负温度依赖性和正压力效应。在实验条件下，预测值与实验结果吻合良好。此外，预测的分支比清楚地表明，在低温下主要产物通道是FC(O)NO的形成，在高温(>500 K)下是FNO + CO的形成。
