Ground and excited potential energy surfaces for CaF+Ca interactions and isotope exchange reactions

TL;DR

This study computes detailed potential energy surfaces for CaF and Ca interactions in various electronic states to understand atom-exchange reactions, revealing deep, anisotropic, and bound states, including an excited state below the ground asymptote.

Contribution

It provides high-level ab initio potential energy surfaces for CaF+Ca interactions in multiple electronic states, including excited states, which is novel for understanding reaction pathways.

Findings

Ground state is deep and highly anisotropic.

Excited states are strongly bound.

One excited state lies below the ground asymptote.

Abstract

We investigate the intermolecular interactions between laser-cooled CaF and Ca, in their ground and excited electronic states, aiming to understand atom-exchange reaction pathways. Using state-of-the-art \textit{ab initio} quantum chemistry methods, we compute potential energy surfaces for nine electronic states arising from the lowest three asymptotes of Ca$_2$F trimer, within the rigid rotor approximation applied to CaF. Two-dimensional potential energy surfaces are computed for the ground state and one of the excited states. We use a combination of the coupled cluster method restricted to single, double, and perturbative triple excitations, and the multireference configuration interaction method with single and double excitations. The ground (X)~$^2\mathrm{A}'$ electronic state of the trimer is significantly deep and highly anisotropic. The excited electronic states are also strongly bound. Notably, the potential energy surface of one of the excited states, (2)~$^2\mathrm{A}'$, lies below the ground-state asymptote of the trimer. By analyzing the potential energy surfaces, we discuss atom-exchange reaction pathways involving both the ground-state interaction between CaF and Ca and the excited metastable state of Ca.