Non-adiabatic mass-correction functions and rovibrational states of $^4$He$_2^+$ ($X\ ^2\Sigma_\text{u}^+$)

TL;DR

This paper calculates non-adiabatic mass-correction functions for $^4$He$_2^+$ using advanced variational methods, leading to highly accurate rovibrational energy levels that align well with experimental data.

Contribution

It introduces a novel computational approach for non-adiabatic mass corrections in $^4$He$_2^+$, improving theoretical predictions of rovibrational states.

Findings

Enhanced agreement with high-resolution spectroscopic data

Accurate computation of nine rotational and two rovibrational intervals

Demonstration of the effectiveness of coordinate-dependent mass corrections

Abstract

The mass-correction functions in the second-order non-adiabatic Hamiltonian are computed for the $^4$He$^+_2$ molecular ion using the variational method, floating explicitly correlated Gaussian functions, and a general coordinate-transformation formalism. When non-adiabatic rovibrational energy levels are computed using these (coordinate-dependent) mass-correction functions and a highly accurate potential energy and diagonal Born-Oppenheimer correction curve, significantly improved theoretical results are obtained for the nine rotational and two rovibrational intervals known from high-resolution spectroscopy experiments.