Acta Phys. -Chim. Sin. ›› 2004, Vol. 20 ›› Issue (04): 400-404.doi: 10.3866/PKU.WHXB20040414

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

Zhai Zhi-Cai;Bai Yun-Shan;Wang Zun-Yao;Wang Lian-Sheng   

  1. School of the Environment, Nanjing University, Nanjing 210093;Department of Chemical Engineering, Yancheng Institute of Technology, Yancheng 224003
  • Received:2003-10-27 Revised:2003-12-16 Published:2004-04-15
  • Contact: Wang Zun-Yao

Abstract: 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.

Key words: Bromine, Hydrogen iodide, Density functional theory(DFT) method,  Reaction mechanism, Bimolicular reaction