The observation of quantum bottleneck states

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.