Ab initio study of the mechanism for the thermal decomposition of the phenoxy radical
Ab initio study of the mechanism for the thermal decomposition of the phenoxy radical
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DOI：
10.1021/jp953566w
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发表时间：
1996-05-30
影响因子：
--
通讯作者：
Liu, MC
中科院分区：
文献类型：
--
作者：
Liu, RF;Morokuma, L;Liu, MC
各种从头算方法已被应用于苯氧基低空电子态的分子结构和能量学及其热分解机理的研究。计算证实了先前从实验考虑中提出的分解机制I（方案1）。它包括双环中间体E2的形成，随后α - cc键裂解生成E3，后者消除CO基团生成主要反应产物C5H5 + CO，速率决定步骤为E2—> E3，过渡态为T2。最佳G2M（rcc,MP2）水平下的活化能为52 kcal/mol，比实验结果高8 kcal/mol。对分解反应进行了多步RRKM计算。理论速率常数在较低温度（T < 1200 K）下与实验结果吻合较好，但在1300 K以上时与实验结果存在偏差。对这种偏差的合理原因进行了讨论。在特定状态和平均状态的CASSCF计算的基础上，已经分配了观察到的苯氧基的电子跃迁。
Various ab initio methods have been applied to the studies of the molecular structure and energetics for the low-lying electronic states of the phenoxy radical and of the mechanism of its thermal decomposition. The calculations confirm the decomposition mechanism I (Scheme 1) suggested earlier from experimental consideration. It involves the formation of the bicyclic intermediate E2 followed by alpha-CC bond cleavage to produce E3 and the elimination of the CO group from the latter leading to the main reaction products, C5H5 + CO. The rate-determining step is E2 --> E3 with transition stale T2. The activation energy, 52 kcal/mol, at our best G2M(rcc,MP2) level, is 8 kcal/mol higher than the value derived from experiment. A multistep RRKM calculation has been performed for the decomposition reaction. The theoretical rate constants agree well with the experimental results at lower temperatures (T < 1200 K) but deviate rom experiment above 1300 K. Plausible reasons fur the deviation have been discussed. On the basis of state-specific and state-averaged CASSCF calculations, the observed electronic transitions for the phenoxy radical have been assigned.