热裂解链引发-终止反应的计算——C—H键的断裂-形成

Calculation for Chain Initiation-Termination Reactions in Thermal Cracking:Cleavage-Formation of C—H Bond

依据正则变分过渡态理论,采用量化计算软件(Gaussian03)详细计算了反应C2H6 C2H5.+H.的速率常数。反应途径上的势能由CBS-Q/6a-611g(d,p)局部构型优化计算得到;反应途径上的振动频率及转动惯量由QC ISD/6-311g(d,p)局部构型优化计算得到。计算结果表明,L ippincott函数与采用CBS-Q方法计算所得的反应途径上的势能值吻合较好,而3次多项式能较好地反映反应途径上的转动惯量的变化。根据计算所得的反应途径上的振动频率拟合出解析函数。根据这些函数,将计算推广应用到烷烃的C—H键断裂反应及其逆反应,以达到简化计算的目的。

Canonical variational transition state theory had been employed in detailed calculations for rate constant of C2H6=C2H5· ＋ H· reaction using quantum chemistry programme Gaussian03. Potential energies along reaction path were calculated based on partial geometry optimization calculations at CBS-Q/6-311g （d, p ）level, while vibration frequencies and rotational inertia along reaction path were calculated at QCISD/6-311 g （ d, p） level. The results showed that potential energy calculated at CBS-Q level agreed well with that based on Lippincott function, and cubic polynomial could be used to correctly describe variation of rotational inertia along the reaction path. Furthermore, analytic functions were proposed on basis of calculated data of vibration frequencies along reaction path. Calculations of C—H bond cleavage reactions of paraffin could be simplified with these functions.