Br_2+Cl_2=2BrCl反应机理的理论和实验研究

Theoretical and Experimental Study on the Reaction Mechanism of Br_2+Cl_2=2BrCl

用(U)MP2方法,取6-311G*基组,研究了反应Br2+Cl2=2BrCl的机理,求得四中心和三中心的过渡态,通过比较反应通道的活化能的大小,得到如下结论:双分子基元反应的最小活化能小于Cl2和Br2的离解能,在没有光引发的条件下,标题反应将以分子与分子作用形式完成;若有光引发,Br2或Cl2先解离成原子,再经过Br原子与Cl2反应或Cl原子与Br2反应,能较快完成标题反应.分别测定了光照和避光两种条件下的反应体系在412nm处吸光度的变化,证实了理论研究的结果.

The gas phase reaction mechanism of Br2＋Cl2=2BrCl had been investigated by （U）MP2 at 6-311G^＊ level, and a series of four-centered and three-centered transition states were obtained. Comparing the activation energies of three reaction paths, the result was achieved as follows： the minimum activation energy of the bimolecular elementary reaction Br2＋Cl2=2BrCl was less than the dissociation energies of Br2 and Cl2. It was thus theoretically proved that the titled reaction occured more easily in the bimolecular form without light initiation. However, if the reaction system was initiated by light, the titled reaction was completed quickly through the reaction path of Br atom reacting with Cl2 or Cl atom reacting with Br2. The theoretical result was further verified by determination of the absorbency （with or without light initiation） at 412 nm.