Semiclassical Transition-State Theory Based on Fourth-Order Vibrational Perturbation Theory: The Symmetrical Eckart Barrier

Semiclassical transition-state theory based on fourth-order vibrational perturbation theory (VPT4-SCTST) is applied to compute the barrier transmission coefficient for the symmetric Eckart potential. For a barrier parametrized to mimic the H2 + H exchange reaction, the results obtained are in excell...

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Veröffentlicht in:The journal of physical chemistry letters 2016-07, Vol.7 (14), p.2708-2713
1. Verfasser: Stanton, John F
Format: Artikel
Sprache:eng
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Zusammenfassung:Semiclassical transition-state theory based on fourth-order vibrational perturbation theory (VPT4-SCTST) is applied to compute the barrier transmission coefficient for the symmetric Eckart potential. For a barrier parametrized to mimic the H2 + H exchange reaction, the results obtained are in excellent agreement with exact quantum calculations over a range of energy that extends down to roughly 1% of the barrier height, V 0, where tunneling is negligible. The VPT2-SCTST treatment, which is commonly used in chemical kinetics studies, also performs quite well but already shows an error of a few percent at ca. 0.8 V 0 where tunneling is still important. This suggests that VPT4-SCTST could offer an improvement over VPT2-SCTST in applications studies. However, the computational effort for VPT4-SCTST treatments of molecules is excessive, and any improvement gained is unlikely to warrant the increased effort. Nevertheless, the treatment of the symmetric Eckart barrier problem here suggests a simple modification of the usual VPT2-SCTST protocol that warrants further investigation.
ISSN:1948-7185
1948-7185
DOI:10.1021/acs.jpclett.6b01239