High-Precision Quantum Dynamics of He$_2$ over the b $^3\Pi_\mathrm{g}$-c $^3\Sigma_\mathrm{g}^+$ Electronic Subspace by including Non-adiabatic, Relativistic and QED Corrections and Couplings

TL;DR

This paper achieves highly precise quantum calculations of helium dimer electronic states, incorporating advanced corrections and couplings, and validates results against experimental data, including predictions for unresolved fine structures.

Contribution

It introduces a comprehensive high-precision quantum model for helium dimer states including non-adiabatic, relativistic, and QED effects with unprecedented accuracy.

Findings

Computed energy levels match high-resolution spectroscopy data.

Predicted fine-structure splittings for unresolved states.

Achieved 1 ppm precision in potential energy curves.

Abstract

Relativistic, quantum electrodynamics, as well as non-adiabatic corrections and couplings, are computed for the b $^3\Pi_\mathrm{g}$ and c $^3\Sigma_\mathrm{g}^+$ electronic states of the helium dimer. The underlying Born-Oppenheimer potential energy curves are converged to 1 ppm ($1:10^6$) relative precision using a variational explicitly correlated Gaussian approach. The quantum nuclear motion is computed over the b $^3\Pi_\mathrm{g}$-c $^3\Sigma_\mathrm{g}^+$ (and B $^1\Pi_\mathrm{g}$-C $^1\Sigma_\mathrm{g}^+$) 9-(12-)dimensional electronic-spin subspace coupled by non-adiabatic and relativistic (magnetic) interactions. The electron's anomalous magnetic moment is also included; its effect is expected to be visible in high-resolution experiments. The computed rovibronic energy intervals are in excellent agreement with available high-resolution spectroscopy data, including the rovibronic b $^3\Pi_\mathrm{g}$-state fine structure. Fine-structure splittings are also predicted for the c $^3\Sigma_\mathrm{g}^+$ levels, which have not been fully resolved experimentally, yet.