From Reactive Rainbow to Dynamic Resonance Well

Abstract

Scattering resonance is a fascinating phenomenon which manifests as a peak or a dip in an observable as a function of collisional energy (E c). Its occurrence requires a potential well to support the resonance states. In this regard, reactive resonance is unusual in that it can exist in a reaction with unbound Born–Oppenheimer potential energy surface, on which the quasi-bound states are dynamically trappedmeaning that some energy is temporarily tied to the other degrees of freedom than the reaction coordinate. The concept of vibrational adiabaticity has been the cornerstone in understanding this phenomenon, for which the vibrationally adiabatic well depth is of primary concern. Recent studies on the F + CH3D reaction have accumulated compelling evidence for a dominant resonance-mediated pathway at low E c as well as for a rainbow feature in pair-correlated angular distribution at higher E c. Here, we report an in-depth study to not only substantiate both claims but also, more importantly, make the first attempt to quantify the vibrationally adiabatic well depth directly from the observed rainbow structure and then compare with the theoretical prediction.

Near-Ambient Pressure Velocity Map Imaging

“…Particle imaging techniques based on Ion Imaging 1 and Velocity Map Imaging (VMI) 2 have revolutionized the field of chemical dynamics, allowing very efficient collection of the velocity distributions of particles coming from a variety of processes. (photodissociation, [1][2][3] photoelectron spectroscopy, 2,4,5 inelastic 6-8 and reactive scattering 9 ) Charged particle-neutral collisions can also be probed [10][11][12] The velocity distributions provide information about the physics underlying and controlling the process of interest. The high collection efficiency is particularly valuable for time-resolved experiments, where many measurements need to be made, and for low count rate experiments.…”