Ab initio mechanism and multichannel RRKM-TST rate constant for the reaction of Cl(2P) with CH2CO (ketene)
Ab initio mechanism and multichannel RRKM-TST rate constant for the reaction of Cl(2P) with CH2CO (ketene)
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DOI：
10.1021/jp992829
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发表时间：
2000-01-20
影响因子：
2.9
通讯作者：
Gu, YS
中科院分区：
文献类型：
--
作者：
Hou, H;Wang, BS;Gu, YS
用从头算G2（MP2）方法研究了氯（P-2）与烯酮反应最重要途径的势能面。在UMP2(full)/6-31G（d,p）能级上，各种可能的配合物和鞍状涂料沿着最小能量反应路径进行了表征。计算结果表明，Cl + CH2CO反应以加消机制为主，直接吸氢途径可以忽略不计。有趣的是，加成反应始于P - π络合物（P - π C）的形成，随后通过P - π C的异构化形成氯化乙酰基自由基CH2ClCO（(2) a’）和氯甲酰基甲基自由基CH2CClO（(2) a’）。CH2ClCO（(2) a’）的C-C键断裂导致产物CO和CH2Cl。通过高能量势垒（TS3）和弱键氢键（HBC1）， P - pi - C的三中心HCl消去被认为是实验观察到的HCl + HCCO产率低的原因。利用从头算数据对各通道的总速率常数和个别速率常数进行了多通道RRKM-TST计算。通过拟合295 K时已知的实验速率常数，确定了无障反应入口的“松散过渡态”。本文的动力学计算可以合理地解释以往的实验结果。在300 ~ 1500 K和新西兰大气压力范围内，总速率常数与温度呈负相关，可拟合为K (T) （1.0 +/- 0.2） × 10(-15)T(-1.58+/-0.02) exp(-565 +/- 2/T) cm(3)分子（-1）s（-1）。同时，速率常数在10(3)~ 10(8)Torr压力范围内表现出典型的下降行为。在较低的压力下（p10 (8) Torr）， ppi C的稳定性主导了反应。发现在脱落区可检测到CH2ClCO（(2)A’）和CH2CClO（(2)A’）两种自由基产物。
The potential energy surface for the most important pathways of the reaction between Cl(P-2) and ketene has been studied using the ab initio G2(MP2) method. A variety of possible complexes and saddle paints along the minimum energy reaction paths have been characterized at the UMP2(full)/6-31G(d,p) level. The calculations reveal that the addition-elimination mechanism dominates the Cl + CH2CO reaction and the direct hydrogen abstraction pathway is negligible. It-is interesting to note that the addition reaction starts by the formation of a p-pi complex (P pi C), and subsequently the chlorinated acetyl radical CH2ClCO((2)A') and the chloroformyl methyl radical CH2CClO((2)A ") are formed through the isomerization of P pi C. The C-C bond scission of CH2ClCO((2)A') leads to the products CO and CH2Cl. The three-center HCl elimination from P pi C, occurring via a high energy barrier (TS3) and a weakly bound hydrogen bonding (HBC1), was proposed to account for the minor yield of the HCl + HCCO observed experimentally. Multichannel RRKM-TST calculation has been carried out for the total and individual rate constants for various channels using the ab initio data. The "loose transition state" in the barrierless reaction entrance was determined by fitting the known experimental rate constant at 295 K. The kinetic calculations in this work can explain reasonably all the previous experimental results. In the temperature range 300-1500 K and the atmospheric pressure of NZ, the total rate constants exhibit negative temperature dependence and can be fitted to the expression k(T) (1.0 +/- 0.2) x 10(-15)T(-1.58+/-0.02) exp(-565 +/- 2/T) cm(3) molecule(-1) s(-1). Meanwhile, the rate constants show the typical fall-off behavior in the pressure range 10(3)-10(8) Torr. At lower pressures (P 10(8) Torr), the stabilization of P pi C dominates the reaction. It is found that two radical products, namely CH2ClCO((2)A') and CH2CClO((2)A "), might be detectable in the fall-off region.