Article
Quantum instanton evaluation of the thermal rate constants and kinetic isotope effects for SiH4+H > SiH3+H2 reaction in full Cartesian space
Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.
The Journal of Chemical Physics
(Impact Factor: 3.12).
04/2007;
126(11):114307.
DOI: 10.1063/1.2714510
Source: PubMed

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ABSTRACT: A simple method to find the instanton trajectories is developed. This method does not employ any approximation and ‘exact’ instanton trajectories have been located for several collinear symmetric reactions. Underlying the method is the notion of stability of periodic trajectories and the behavior of the action derivatives. Applications to thermal rate constants calculations are presented showing that the method is suitable for quantitative rate constant predictions. In the deep tunneling regime, where a classical rate underestimation is about two orders of magnitude, the semiclassical instanton rate is within a few percent of the exact quantum mechanical value. Then, the consistent amount of tunneling involved in the heavy particle transfer, as for the collinear H+BrH reaction, shows that ‘cornercutting’ is not necessary for tunneling to occur, even if it is a sufficient condition to detect a significant presence of tunneling effects.Molecular Physics 05/2012; 110(910):547. DOI:10.1080/00268976.2012.663943 · 1.64 Impact Factor 
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ABSTRACT: The dissociation and recombination rates of physisorbed H2, and the total dissociation rate of gas phase H2 on the rigid Ni(100) surface, as well as the corresponding kinetic isotope effects, are calculated by using the quantum instanton method, together with path integral Monte Carlo and adaptive umbrella sampling techniques. Both the dissociation and recombination rates of physisorbed H2 are dramatically enhanced by the quantum motions of H2 at low temperatures, for instance, the quantum rates are 43 and 7.5 times larger than the classical ones at 200 K, respectively. For the dissociation of gas phase H2, at high temperatures, the H2 can fly over the physisorbed state and dissociate directly, however, at low temperatures, the H2 is first physisorbed and then dissociates under steady state approximation. The total dissociation rate of gas phase H2 can be expressed as a combination of the direct and steady state dissociation rates. It has the form of an inverted bell with a minimum value at about 400 K, and detailed analysis shows that the dissociation of gas phase H2 is dominated by a steady state process below 400 K, however, both the steady state and direct processes are important above 400 K. The calculated kinetic isotope effects reveal that H2 always has larger rates than D2 no matter which dissociative process they undergo.Physical Chemistry Chemical Physics 05/2014; 16(26). DOI:10.1039/c4cp01705f · 4.20 Impact Factor 
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ABSTRACT: The rate constants and kinetic isotope effects of H2 dissociation and recombination on Ni(100) surface are calculated by using the quantum instanton method, together with path integral Monte Carlo and adaptive umbrella sampling techniques. The Ni(100) surface model containing 104 nickel atoms and the potential energy surface based on the embedded diatomics in molecules are used. For the H2 dissociation, the results on the rigid lattice are consistent with experimental data. Compared to the rigid lattice, the classical and quantum motions of the lattice further enhance the dissociation rates by 18 and 49% at 300 K. The calculated kinetic isotope effects show that the H2 always has the largest rate, while the D2 has the smallest one. For the H2 recombination, however, the effects of lattice motions on the rates are different from those for the dissociation, that is, compared to the rigid lattice, both the classical and quantum motions of the lattice lower the recombination rates. The possible mechanism is analyzed by the corresponding free energy profiles.The Journal of Physical Chemistry C 09/2013; 117(37):19010–19019. DOI:10.1021/jp406000f · 4.84 Impact Factor
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