A new connection between the absorption spectrum of hydrogen and the many lined spectrum

Dieke and Hopfield showed that the absorption bands of H2 , which are located in the extreme ultra-violet (about 1000-1500 Å. U.) were due to transitions up from the ground level of H2 , which they called A, to two higher electronic levels which they called B and C respectively. Two years ago I found the emission bands which go down to the B level and some of them were described and partially analysed in this journal. In a series of papers Dr. Davidson and I have been able to show that these bands comprise a large number of distinct band systems and contain a very large part of the total strength of the visible emission spectrum of H2 . In previous papers I have called this B level of Dieke and Hopfield 21 S as it has an effective principal quantum number in the neighbourhood of 2 and its properties are those of an S level. In view of recently proposed changes in the nomenclature for band spectra I propose in this paper to denote this B or 21 S level by the symbol 2p 1 ∑. In this notation 2 denotes the principal quantum number andp indicates that the azimuthal or equivalent quantum number of the excited electron is 1. ∑ means that the component of the total angular momentum (or equivalent quantized quantity) about the internuclear axis is 0 and the prefix1 that the state is a singlet state. Various attempts have been made from time to time to discover bands in this spectrum which end on Dieke and Hopfield’s C level, but, until recently, nothing at all convincing has resulted from these efforts. I have now found a number of band systems which end on this C state.