Rovibrational Computations for the He 2 a 3 Σ u + State Including Nonadiabatic, Relativistic, and QED Corrections

Overview

High-precision rovibrational spectroscopy calculations are performed for the metastable a 3Σu+ electronic state of the He2 dimer. A potential energy curve is established with sub-ppm accuracy through incorporation of relativistic effects, quantum electrodynamic corrections, and nonadiabatic coupling terms. The work addresses the fundamental problem of computing highly accurate molecular energy levels when multiple physical corrections operate at significant magnitudes.

Methods and approach

A potential energy curve for the a 3Σu+ state is generated with relativistic and QED corrections applied to achieve fractional ppm accuracy. The nuclear Schrödinger equation is solved on this surface using diagonal Born-Oppenheimer corrections and nonadiabatic mass corrections to obtain rovibrational eigenvalues. The computational framework systematically accounts for corrections spanning multiple orders of magnitude in their energetic contributions.

Key Findings

Computed rovibrational intervals and fine-structure splittings are compared against high-resolution spectroscopic data across a wide energy range. The calculations demonstrate remarkable agreement with experimental observations. The approach successfully reconciles the contributions from relativistic effects, QED corrections, and nonadiabatic phenomena within a unified computational framework.

Implications

The attainment of sub-ppm accuracy in the potential energy curve combined with systematic treatment of nonadiabatic and relativistic corrections establishes a reference standard for He2 a 3Σu+ spectroscopy. The methodology extends the precision frontier for molecular calculations by carefully controlling all dominant physical contributions. Results validate the computational protocols for systems requiring simultaneous treatment of multiple quantum corrections.