First-principle interaction potentials for metastable He($^3$S) and Ne($^3$P) with closed-shell molecules. Application to Penning-Ionizing systems

TL;DR

This study develops first-principle interaction potentials for metastable helium and neon with closed-shell molecules, using two computational methods, and compares results with experimental data to understand Penning ionization processes.

Contribution

The paper introduces new first-principle potential curves for metastable He and Ne interacting with molecules, applying both CC and SAPT methods, and compares them with experimental results.

Findings

Good agreement with recent scattering experiments.

Ne systems show minimal orbital angular momentum anisotropy.

SAPT successfully describes Ne*–Ar interactions, while CC diverges for this system.

Abstract

We present new interaction potential curves, calculated from first-principle, for the He$(^3$S)$...$H$_2$ and He$(^3$S)$...$Ar systems, relevant in Penning's ionization experiments. Two different approaches were applied: supermolecular using coupled cluster theory (CC) and perturbational within symmetry-adapted perturbation theory (SAPT). Both methods gave consistent results and the potentials were used to determine the positions of shape resonances in low collision energy scattering regime. We found a good agreement with the most recent scattering experiment of Henson {\em et al.} [Science {\bf 338}, 234 (2012)]. In addition, we investigated two other dimers, composed of metastable Ne and ground state He and Ar atoms. For the Ne$(^3$P)$...$He system a good agreement between CC and SAPT approaches was obtained. The Ne$(^3$P)$...$Ar dimer was described only with SAPT, as CC gave divergent results. Ne$^*$ systems exhibit extremely small electronic orbital angular momentum anisotropy of the potentials. We attribute this effect to the screening of the open 2$p$ shell by the singly occupied 3$s$ shell.