Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 7, Issue 14, Pages 2708-2713Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.6b01239
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Funding
- U.S. Air Force Office of Scientific Research [A9550-12-1-0483]
- U.S. National Science Foundation [CHE-1361031]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1361031] Funding Source: National Science Foundation
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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 H-2 + 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.
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