The observation of quantum bottleneck states

Abstract

The concept of quantum bottleneck states near reaction barriers is essential to the elucidation of chemical reaction rates and reaction dynamics. Recent studies of the dynamics of simple gas-phase chemical reactions have revealed that the transition state controls the detailed observable characteristics of a reaction to a far greater degree than was generally imagined. However, observation of such quantum bottleneck states is extremely difficult. In this article, we provide a review of the current status of observing these quantum bottleneck states in both bimolecular and unimolecular reactions, providing an updated picture of the concept of quantum bottleneck states in chemical reactions.

A quasiclassical trajectory study of the time-delayed forward scattering in the hydrogen exchange reaction

“…QCT cannot detect resonances or QBSs, but the symmetric stretches and bends described here for the forward scattered trajectories are consistent with the complex motions predicted for both resonances 13 and QBS. 4,10 The dominant classical mechanism, which controls scattering into the outer spiral of the QCT snapshots ͑Fig. 2͒, progresses from hard collinear impacts to glancing impacts.…”

“…Some believe that it is due to Feshbach resonances, in which the H 3 collision complex is trapped in a well of an effective potential, 8,13 while others believe that QBSs, a series of effective reaction barriers at the TS, are responsible. 4,9,10 Note that the latter does not require a well in the effective potential and that, as in the classical analog, the time delay is caused by the slowing down of the atoms at the top of the effective barrier. 6 Quasiclassical trajectory ͑QCT͒ calculations have long been used to understand the dynamics of chemical reactions.…”

Theoretical studies on bimolecular reaction dynamics

“…It is seen that these distributions have an oscillatory structure. This structure is associated with the interference between quantum scattering states that have energies close to the effective barriers for different internal states at the transition state (6). These quantum barrier states have been invoked in many studies of chemical kinetics including modern transition-state theory (7) and the classic Rice-Ramsperger-Kassel- Marcus theory of unimolecular reactions (8).…”

Chemistry at surfaces: from ab initio structures to quantum dynamics

“…For gas-phase systems, for example, quantization of the internal modes at the transition state (quantized transition states or quantized dynamical bottlenecks) or Feshbach resonances on purely repulsive potential energy surfaces are typical quantum effects that have been predicted for several collision systems, but that have been observed only for a few of them. The H + H 2 isotopic family of reactions is the best known example for quantized dynamical bottlenecks which lead to an observable time-delayed mechanism [147,148], and interference features [149,150]. The F + HD→HF + D reaction is the first reaction for which conclusive evidence has been found for a Feshbach resonance in a full collisional dynamics [151,152] and only recently experimental evidence has been found for some polyatomic reactions [153][154][155].…”