Transmission Coefficients for Chemical Reactions with Multiple States: Role of Quantum Decoherence
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- 作者：Aur茅lien de la Lande ; Jan 艠ez谩膷 ; Bernard L茅vy ; Barry C. Sanders ; Dennis R. Salahub
- 刊名：Journal of the American Chemical Society
- 出版年：2011
- 出版时间：March 23, 2011
- 年：2011
- 卷：133
- 期：11
- 页码：3883-3894
- 全文大小：1084K
- 年卷期：v.133,no.11(March 23, 2011)
- ISSN：1520-5126
文摘
Transition-state theory (TST) is a widely accepted paradigm for rationalizing the kinetics of chemical reactions involving one potential energy surface (PES). Multiple PES reaction rate constants can also be estimated within semiclassical approaches provided the hopping probability between the quantum states is taken into account when determining the transmission coefficient. In the Marcus theory of electron transfer, this hopping probability was historically calculated with models such as Landau鈭抁ener theory. Although the hopping probability is intimately related to the question of the transition from the fully quantum to the semiclassical description, this issue is not adequately handled in physicochemical models commonly in use. In particular, quantum nuclear effects such as decoherence or dephasing are not present in the rate constant expressions. Retaining the convenient semiclassical picture, we include these effects through the introduction of a phenomenological quantum decoherence function. A simple modification to the usual TST rate constant expression is proposed: in addition to the electronic coupling, a characteristic decoherence time 蟿dec now also appears as a key parameter of the rate constant. This new parameter captures the idea that molecular systems, although intrinsically obeying quantum mechanical laws, behave semiclassically after a finite but nonzero amount of time (蟿dec). This new degree of freedom allows a fresh look at the underlying physics of chemical reactions involving more than one quantum state. The ability of the proposed formula to describe the main physical lines of the phenomenon is confirmed by comparison with results obtained from density functional theory molecular dynamics simulations for a triplet to singlet transition within a copper dioxygen adduct relevant to the question of dioxygen activation by copper monooxygenases.