Control of chemical reactivity by transition-state and beyond

Abstract

State-specific reaction dynamics is largely controlled by transition state.

State‐to‐state quantum reactive scattering in four‐atom systems

“…This surprising result contradicts the extended Polanyi rules but can be understood by the SVP model, which suggests that the vibrational modes have stronger coupling with the reaction coordinate at the transition state than the translational mode . This and other examples suggest that the SVP model is more general, particularly for reactions with more than three atoms …”

“…Both models are based on transition‐state properties, thus expected to work best when the reaction is controlled by the transition state. The SVP model has been applied to a number of reactions and the results have been quite promising . In Figure , the projections of reactant and product normal mode vectors onto the reaction coordinate at the transition state are shown for the prototypical X + H 2 O → HX + OH (X = H, F, Cl) reactions.…”

“…With the advent of crossed‐molecular beam and laser techniques, it has become possible to interrogate reactive scattering in energy‐resolved and initial state‐specific manners . These experimental advances have yielded a plethora of quantum‐state resolved information concerning the influence of the PES on reaction dynamics, which sheds light on important issues such as tunneling, mode specificity, resonances, and nonadiabaticity . One of the most detailed measurements of reactivity by a crossed‐molecular beam apparatus is the differential cross section (DCS), namely angular distributions of product internal states.…”

Kinetics of the OH+HCl→H2O+Cl reaction: Rate determining roles of stereodynamics and roaming and of quantum tunneling

“…Using the quasi‐classical trajectory method, the Guo group showed that for the OH + HCl reaction, the vibrational excitation of the HCl reactant greatly increases the reactivity, while the OH vibrational acts essentially as a spectator . This result was indicated as contradicting the Polanyi's rule, which suggests that the translational energy is more efficient than vibrational energy in enhancing an early barrier reaction: the authors elucidated this violation by a sudden vector projection model, which attributes the promotional effect of the HCl vibration mode to its strong coupling with the reaction coordinate at the transition state …”

“…[21] This result was indicated as contradicting the Polanyi's rule, which suggests that the translational energy is more efficient than vibrational energy in enhancing an early barrier reaction: the authors elucidated this violation by a sudden vector projection model, which attributes the promotional effect of the HCl vibration mode to its strong coupling with the reaction coordinate at the transition state. [21][22][23] The present approach Relevant from our view point are the quasi-classical trajectory calculations by Bonnet et al, [24] who demonstrated unexpected reaction pathways involving strong reorientation of the reagents, and showed that the most important channels were far from the minimum energy reaction path. They propose a dynamical extension of the notion of cone of acceptance to rationalize the stereodynamic effects.…”