摘要
用从头算UMP2方法采用 6 3 11+G 基组详细研究了Cl原子与甲酸反应的最佳反应路径 ,对所有驻点都进行了G2单点能校正 ,结果表明 :在Cl与HCOOH反应的过程中 ,Cl原子主要夺取trans HCOOH中C端的H原子 ,产生cis HOCO基团 ,反应的势垒为 16 7kJ/mol.考虑Cl原子存在下的二级反应 ,cis HOCO将通过通道R1a1和R1a2 生成trans HOCOCl再分解为最终产物CO2 .cis HOCO和trans HOCO自由基与Cl原子的反应为放热和无势垒过程 .而HOCO和HOCOCl两个中间体的cis 到trans 转化势垒分别为 15 1和 3 3 5kJ/mol.由于构型的原因 ,HOCOCl分解成CO2 和HCl必须通过trans 构型来进行 .这步反应的势垒较高 ,为 13 1 0kJ/mol.2 98K时 ,采用经典过渡态理论计算得到的引发步骤的H 迁移反应的速率常数与实验值符合很好 .也计算了甲酸二聚体与Cl原子的H 迁移反应的速率常数 .
At the G2 // UMP2/6-311 + G** level, the reaction pathway of Cl with HCOOH oxidation reaction was discussed in this paper. The dominant initial step is Cl atom attacking H on C in trans-formic acid through a barrier hight of 16.7 kJ/mol to form cis-HOCO radical R1a. Two multi-step pathways are related to a secondary reaction of cis-HOCO radical converting to trans-HOCOCl by another Cl atom through the secondary reaction of R1a(1) and R1a(2), then trans-HOCOCl can dissociate to the final product CO(2). For R1a(1) or R1a(2) channel, the adduct forming step has no barrier but the cis to trans conversion step has a small barrier. The final step of dissociation of trans-HOCOCl needs high activation energy of 131.0 kJ/mol at the G2 // UMP2/6-311 + G** level. The calculated TST rate constants of the initial H-abstraction step are in good agreement with the experimental result. The H-abstraction reaction of formic acid dimer with Cl atom was also considered.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2003年第4期499-504,共6页
Acta Chimica Sinica
基金
理论化学与计算国家重点实验室资助项目
