Collisional Quenching at Ultralow Energies: Controlling Efficiency with Internal State Selection

TL;DR

This study models vibrational quenching of excited H₂ molecules colliding with Li⁺ ions at ultralow energies, revealing how initial state selection can control quenching efficiency through quantum scattering phenomena.

Contribution

It provides an exact quantum dynamical analysis linking scattering features to potential properties, suggesting control of quenching via initial state preparation.

Findings

Identification of Ramsauer-Townsend minima in elastic cross sections

Enhanced cooling rates from specific initial vibrational states

Correlation of scattering features with potential at zero energy

Abstract

Calculations have been carried out for the vibrational quenching of excited H$_2$ molecules which collide with Li$^+$ ions at ultralow energies. The dynamics has been treated exactly using the well known quantum coupled-channel expansions over different initial vibrational levels. The overall interaction potential has been obtained from the calculations carried out earlier in our group using highly correlated ab initio methods. The results indicate that specific features of the scattering observables, e.g. the appearance of Ramsauer-Townsend minima in elastic channel cross sections and the marked increase of the cooling rates from specific initial states, can be linked to potential properties at vanishing energies (sign and size of scattering lengths) and to the presence of either virtual states or bound states. The suggestion is made that by selecting the initial state preparation of the molecular partners, the ionic interactions would be amenable to controlling quenching efficiency at ultralow energies.