Poully Benjamin, Bergeat Astrid, Hannachi Yacine
ISM Groupe de Spectroscopie Moléculaire, Université Bordeaux, France.
J Phys Chem A. 2008 Sep 4;112(35):8148-53. doi: 10.1021/jp804504g. Epub 2008 Aug 13.
The different stationary points on the potential energy surface relative to the title reaction have been reinvestigated at the B3LYP/aug-cc-pVDZ level with relative energies computed at the CCSD(T)/aug-cc-pVTZ level with B3LYP/aug-cc-pVDZ optimized geometries and by using the G3B3 composite method. Two entrance channels have been identified. The first one corresponds to boron addition at one of the oxygen atoms of the CO 2 molecule leading to trans-BOCO, which is found to be about 27 kcal/mol exothermic with a potential energy barrier of 16.4 kcal/mol (G3B3). The second channel, which has not been identified in previous theoretical works, corresponds to a direct insertion of the boron atom into a CO bond and leads to OBCO. The B + CO 2 --> OBCO step is found to be about 84 kcal/mol exothermic and needs to overcome a potential energy barrier of only 3.6 kcal/mol (G3B3). The rate constant at 300 K of the insertion step, calculated by using TST theory with G3B3 calculated activation energy value, is 5.4 10 (-14) cm (3) molecule (-1) s (-1), in very good agreement with the experimental data ((7.0 +/- 2.8) 10 (-14) cm (3) molecule (-1) s (-1), DiGiuseppe, T. G.; Davidovits, P. J. Chem. Phys. 1981, 74, 3287). The one corresponding to the addition process is found to be several orders of magnitude smaller because of a much higher potential energy barrier. The addition channel would not contribute to the title reaction even at high temperature. A modified Arrhenius equation has been fitted in the 300-1000 K temperature range, which might be useful for chemical models.
在B3LYP/aug-cc-pVDZ水平上，利用CCSD(T)/aug-cc-pVTZ水平计算的相对能量，并结合B3LYP/aug-cc-pVDZ优化的几何结构，通过使用G3B3复合方法，重新研究了相对于标题反应的势能面上的不同驻点。确定了两个入口通道。第一个通道对应于硼原子加到CO₂分子的一个氧原子上，生成反式-BOCO，发现该反应放热约27 kcal/mol，势能垒为16.4 kcal/mol（G3B3）。第二个通道在以前的理论研究中未被识别，它对应于硼原子直接插入CO键，生成OBCO。发现B + CO₂→OBCO这一步放热约84 kcal/mol，只需克服3.6 kcal/mol的势能垒（G3B3）。使用TST理论并结合G3B3计算的活化能值，计算出300 K时插入步骤的速率常数为5.4×10⁻¹⁴ cm³·分子⁻¹·s⁻¹，与实验数据（(7.0±2.8)×10⁻¹⁴ cm³·分子⁻¹·s⁻¹，DiGiuseppe, T. G.; Davidovits, P. J. Chem. Phys. 1981, 74, 3287）非常吻合。由于势能垒高得多，发现对应于加成过程的速率常数要小几个数量级。即使在高温下，加成通道对标题反应也没有贡献。在300 - 1000 K温度范围内拟合了一个修正的阿伦尼乌斯方程，这可能对化学模型有用。
