Structure of Na(3 2P)–Arn clusters using semiempirical potentials

Abstract

We have calculated the minimum energy geometries of clusters formed by electronically-excited sodium atoms in their (3 2P) state with argon atoms. The potential energy functions needed to describe interactions with an open-shell atom are not pairwise additive. Those used here were constructed using a first-order perturbation treatment. The semiempirical pair potentials used as input were derived from direct spectroscopic evidence, in the case of the A 2Π potential, and indirectly from matrix isolation data for the B 2Σ. We find the clusters to be planar for n=2–5. Additional argon atoms form an argon subcluster, avoiding the perpendicular to the Na*–Ar5 plane. We have investigated the sensitivity of the cluster geometry to variations in the potential parameters, and predict our qualitative conclusions will not be changed by further data on the B potential. We propose a naming convention to clarify discussion of these ring-containing clusters. We have also calculated geometric isomers for the Na*–Ar5 case. The significance of these findings for fluorescence experiments in cryogenic rare gas matrices and other condensed phase experiments is discussed.