Br2+2HI=2HBr＋I2应机理的密度泛函理论

用密度泛函理论(DFT)B3LYP方法，取3-21G**基组研究了气相反应Br2＋2HI=2HBr＋I2的机理，求得一系列四中心和三中心的过渡态.双分子基元反应Br2＋HI→HBr＋IBr和IBr＋HI→I2＋HBr的活化能(81.02和121.08 kJ?mol－1)小于Br2、HI和IBr的解离能(249.21、320.16和232.42 kJ?mol－1)，故从理论上证明了标题反应将优先以分子与分子作用形式分两步完成.同时发现I原子与Br2分子反应生成较稳定的IBr2是一个无能垒过程，IBr2分解为IBr和Br原子的能垒为70.88 kJ?mol－1.

The Reaction Mechanism of Br2 +2HI =2HBr + I2 by Density Functional Theory

The mechanism of reaction Br2＋2HI=2HBr＋I2 has been carefully investigated with density functional theory(DFT) at B3LYP/3-21G** level, and a series of four-centred and three-centred transition states have been obtained. The activation energies of the bimolecular elementary reactions Br2＋HI→HBr＋IBr and IBr＋HI→I2＋HBr(81.02 and 121.08 kJ?mol－1, respectively) are less than the dissociation energy of Br2, HI and IBr(249.21, 320.16, and 232.42 kJ?mol－1). It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form with two medium steps. And it was also found that the reaction of I atom and Br2 to form stable IBr2 molecule is a process without energy barrier, and the energy barrier for decomposition of IBr2 into IBr and Br atom is 70.88 kJ?mol－1.