Spin structure of diatomic van der Waals molecules of alkali atoms

TL;DR

This paper develops a reduced interaction potential model to analyze the spin structure of weakly bound diatomic van der Waals molecules of alkali atoms, capturing key properties across various magnetic fields.

Contribution

It introduces a simplified potential model that accurately describes the spin structure and near-threshold states of alkali diatomic molecules, facilitating computational studies.

Findings

Spin structure variation is due to electronic spin exchange and hyperfine interactions.

A single parameter classifies the spin structure across alkali species.

The model captures properties over a broad magnetic field range.

Abstract

We theoretically investigate the spin structure of weakly bound diatomic van der Waals molecules formed by two identical bosonic alkali atoms. Our studies were performed using known Born-Oppenheimer potentials while developing a reduced interaction potential model. Such reduced potential models are currently a key for solving certain classes of few-body problems of atoms as they decrease the numerical burden on the computation. Although the reduced potentials are significantly shallower than actual Born-Oppenheimer potentials, they still capture the main properties of the near-threshold bound states, including their spin structure, and the scattering states over a broad range of magnetic fields. At zero magnetic field, we find that the variation in spin structure across different alkali species originates from the interplay between electronic spin exchange and hyperfine interactions. To characterize this competition we introduce a single parameter, which is a function of the singlet and triplet scattering lengths, the atomic hyperfine splitting constant, and the molecular binding energy. We show that this parameter can be used to classify the spin structure of vdW molecules for each atomic species.