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首页> 美国政府科技报告 >Ab Initio Predictions and Experimental Confirmation of Large Tunneling Contributions to Rate Constants and Kinetic Isotope Effects for Hydrogen Atom Transfer Reactions
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Ab Initio Predictions and Experimental Confirmation of Large Tunneling Contributions to Rate Constants and Kinetic Isotope Effects for Hydrogen Atom Transfer Reactions

机译：大型隧道对速率常数的贡献和氢原子转移反应的动力学同位素效应的从头算预测和实验证实

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The importance of tunneling in gas-phase hydrogen-atom transfer reactions is investigated. New experimental measurements and theoretical calculations are presented for the intramolecular kinetic isotope effect K usb 3/K sub 4. This new information and earlier results for the reaction rate constants fot the O + H2 and O + D2 reactions provide strong evidence for the dominance of tunneling in all four reactions at temperatures below 500K. Three theoretical approaches are used: the improved canonical variational theory with classical reaction coordinate motion (ICVT), ICVT with least-action ground-state transmission coefficients to account for tunneling (ICVT/LAG), and the reduced-dimensionally quantum calculations with an adiabatic incorporation of bending motion (denoted more specifically as collinear exact quantum with ground-state bend or CEQB/G). All calculations use an accurate ab initio potential energy surface. In general the agreement is good between the ICVT/LAG and CEQB/G calculations and the experimental results. Although the ICVT results (which neglect tunneling effects) are accurate at high temperatures (1400-1900K), they are inconsistent with the experimental results temperatures (318-500K) indicating that tunneling is important. The LAG method also provides a measure of the importance of tunneling for this reaction: the percentage of the reaction that occurs by tunneling. Fo the O + H2 reaction this factor is 94% and 76% at 300 and 400K, respectively.

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