三甲基铝双聚体和单体的气相离解-缔合平衡模拟计算

在B3LYP/6-31l++G(3df, 2pd)水平上全优化得到了三甲基铝双聚体(d-TMA)的C2h和C2v两种构型和单体的C3h结构. 着重用完全基组方法CBS-4M模拟计算了TMA气相平衡中各物种在1.01×105 Pa和300～550 K范围内的热力学函数值. 通过考察d-TMA三线态构型和异裂反应对系统熵值的影响, 准确计算了d-TMA离解反应的ΔrHm和ΔrSm. 以lnKd对1/T作图, 两者之间具有很好的线性关系: lnKd=−9624.4363/T+20.2303, 相关系数R2=1.0000, 与前人实验结果相当一致. 在此基础上提出了新的d-TMA气相离解-缔合反应机理.

Simulating Calculation of the Dissociation-Association Equilibrium of Dimer and Monomer of Trimethylaluminum in Gas Phase

Both the C2h and C2v configurations of trimethylaluminum dimer (d-TMA) and the C3h structure of monomer were obtained by full optimization at B3LYP/6-311++G(3df, 2pd) level. With Complete Basis Set method CBS-4M as emphasis, the thermodynamic function values of each species of TMA in gas-phase equilibrium at 1.01×105 Pa and in the range of 300～550 K were calculated by simulation. Through the consideration of the triplet-state configuration of d-TMA and the effect of heterolytic reaction on system entropy value, ΔrHm and ΔrSm of the dissociation reaction of d-TMA were accurately calculated at the same time. The plot of lnKd vs 1/T had a perfectly linear relation: lnKd=−9624.4363/T+20.2303, and the correlation coefficient R2=1.0000, which agreed quite well with the predecessors′ experimental results. Based upon these findings, a new dissociation-association reaction mechanism of d-TMA in gas phase was proposed.