Rovibrational Computations for the He2 a 3Σu+ State Including Nonadiabatic, Relativistic, and QED Corrections

A potential energy curve (PEC) accurate to a fraction of 1 ppm (1:106) is computed for the a 3Σu+ state of He2 endowed with relativistic and QED corrections. The nuclear Schrödinger equation is solved on this PEC with diagonal Born–Oppenheimer and nonadiabatic mass corrections to obtain highly accurate rotational–vibrational levels. The computed rovibrational intervals and fine-structure splittings, spanning over several orders of magnitude in energy, are found to be in remarkable agreement with available high-resolution spectroscopy data.