Long-range forces between two excited mercury atoms and associative ionization

TL;DR

This paper calculates the long-range quadrupole-quadrupole and dispersion interactions between excited mercury atoms, which are crucial for understanding associative ionization processes in various collision regimes.

Contribution

It provides ab initio calculations of long-range interactions between excited Hg atoms and improves estimates of chemi-ionization cross sections.

Findings

Interactions vary significantly between different atomic pairs.

Long-range forces influence associative ionization rates.

Results aid in modeling cold and thermal collision processes.

Abstract

The long-range quadrupole-quadrupole ($\sim R^{-5}$) and leading dispersion ($\sim R^{-6}$) interactions between all pairs of excited Hg($6s6p$) $^3P_0$, $^3P_1$, $^3P_2$, and $^1P_1$ atoms are determined. The quadrupole moments are calculated using the {\it ab initio} relativistic configuration-interaction method coupled with many-body perturbation theory. The van der Waals coefficients are approximated using previously calculated static polarizabilities and expressions for the dispersion energy that are validated with similar systems. The long-range interactions are critical for associative ionization in thermal and cold collisions, and are found to be quite different for different pairs of interacting states. Based on this knowledge and the short-range parts of previously calculated potential curves, improved estimates of the chemi-ionization cross sections are obtained.