The light from near the electrodes of an ac glow discharge in helium is found to be particularly rich in the He2 spectrum. This light occurs at an unusual phase of the voltage cycle.
The process which forms excited molecules also gives rise to excited atoms. Furthermore, the process is inhibited by the presence of an electric field.
There are indications that the process is one of recombination between electrons and atomic positive ions.
W. D. PARKINSON, "The Formation of Molecular Helium in a Glow Discharge," J. Opt. Soc. Am. 41, 619-622 (1951)