The fine structure of the spectral lines of H 2 : measurements with a reflexion echelon

The fine structure of the lines of the H2 spectrum was discovered by Richardson & Williams in 1931, and a short account of their observations was published in a letter to Nature at the time. Since then no further publication on the subject has appeared. The present paper represents the results of experiments and observations made during the last six years with improved apparatus, including the Royal Society’s 40 plate reflexion echelon. About 250 lines at the red end of the visible spectrum have been examined and their fine structures photographed and measured. These include most of the important lines of the triplet systems 3p 3 Π → 2s 3 Σ and 3d 3 ΠΣΔ → 2p 3 Π , as well as important lines of the system 3s 3 Σ → 2p 3 Π and 3Y → 2s 3 Σ , together with some lines of the triplet system 3p 3 Σ → 2s 3 Σ . The singlets are represented by about 20 lines coming from the states 3d 1 Σ , 3d 1 Πd , 3s 1 Σ , 2s 1 Σ , 31 K ,1 M , and1 N and ending in 2p 1 Σ or belonging to the system 3p 1 Π → 2s 1 Σ . There is also a small proportion of unclassified lines. The present paper is limited to a descriptive account of the observations and the analysis and tabulation of the data obtained. The analysis of these data has already been carried out and the results will be published separately. The plate which reproduces a photograph of the crossed spectra of the stronger lines dealt with is the first published picture showing the fine structure under consideration.