The Hydrogen-Iodine Reactions: 100 Years Later
Max Bodenstein opened the field of gas phase chemical kinetics in 1894 with his report of experimental studies of the hydrogen-iodine reaction H2 + I2 → HI + HI and its reverse HI + HI → H2 + I2. Bodenstein measured the rates of the forward and reverse reactions, their equilibria, and their temperature dependence. He found second order kinetic expressions and an Arrhenius temperature dependence for the rate constants. He suggested several mechanisms for these reactions.
Modern theoretical and experimental studies have revealed additional details of the reaction kinetics. The results of these studies suggest that the low temperature thermal reaction proceeds by both the direct bimolecular reaction of hydrogen molecules with vibrationally excited iodine molecules H2 + I2 (hi v) → HI + HI and the termolecular reaction of hydrogen molecules with iodine atoms H2 + I + I → HI + HI. The direct bimolecular reaction mechanism and the termolecular reaction mechanism were among those suggested by Bodenstein one hundred years ago.
KeywordsPotential Energy Surface Vibrational Excitation Iodine Atom Collinear Region Arrhenius Temperature Dependence
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