Rotational cooling efficiency upon molecular ionization: the case of Li$_2(a^3\Sigma_u^+)$ and Li$_2^+(X^2\Sigma_g^+)$ interacting with $^4$He

TL;DR

This study calculates low-temperature collisional excitation cross sections for Li₂ and Li₂⁺ molecules with helium, revealing structural influences on inelastic flux distributions and rotational cooling efficiency upon ionization.

Contribution

It provides the first detailed quantum dynamical analysis of collisional excitation for both neutral and ionic lithium dimers with helium at low temperatures.

Findings

Similar inelastic flux distributions in neutral and ionic systems.

Structural changes in molecular rotor features affect collisional outcomes.

Ionization impacts rotational cooling efficiency.

Abstract

The low-temperature (up to about 100K) collisional (de)excitation cross sections are computed using the full coupled-channel (CC) quantum dynamics for both Li$_2$ and Li$_2^+$ molecular targets in collision with $^4$He. The interaction forces are obtained from fairly accurate {\it ab initio} calculations and the corresponding pseudo-rates are also computed. The results show surprising similarities between sizes of inelastic flux distributions within final states in both systems and the findings are connected with the structural change in the molecular rotor features when the neutral species is replaced by its ionic counterpart.