The Wigner-Witmer diatomic eigenfunction

TL;DR

This paper revisits the exact eigenfunction for diatomic molecules derived by Wigner and Witmer, providing a symmetry-based derivation crucial for accurate spectral predictions and diagnostics.

Contribution

It offers a symmetry-based derivation of the Wigner-Witmer diatomic eigenfunction, highlighting its importance for molecular spectral analysis.

Findings

Derived the exact diatomic eigenfunction using fundamental symmetries

Validated spectral predictions against recorded laser-induced plasma spectra

Enhanced understanding of diatomic molecular eigenfunctions

Abstract

Born and Oppenheimer reported an approximate separation of molecular eigenfunctions into electronic, vibrational, and rotational parts, but at the end of their paper showed that the two angles describing rotation of the nuclei in a diatomic molecule are exactly separable. A year later in a two-part work devoted strictly to diatomic molecules, Wigner and Witmer published (1) an exact diatomic eigenfunction and (2) the rules correlating the electronic state of a diatomic molecule to the orbital and spin momenta of the separated atoms. The second part of the Wigner-Witmer paper became famous for its correlation rules, but, oddly, the exact eigenfunction from which their rules were obtained received hardly any attention. Using three fundamental symmetries, we give a derivation of the Wigner-Witmer diatomic eigenfunction. Applications of our derivations are fundamental to predicting accurate diatomic molecular spectra that we compare with recorded spectra for diagnostic purposes, such as measurements of molecular spectra following generation of laser-induced plasma.