The fine structure of the helium arc spectrum

Abstract

Ever since its discovery the spectrum of helium has been thought to consist of singlets and doublets. Recently, however, spectroscopic theory has indicated that it should consist of singlets and triplets since helium is a two-electron system. Various attempts have been made to resolve the doublets into triplets,(1) but up to the present there have been no conclusive results. Within the last few months interest has been revived in these lines by the theoretical work of Heisenberg,(2) which predicts a triplet structure with unusual separation ratios. It is now possible to show that the helium lines really have a structure similar to that predicted by Heisenberg.