Characteristics of the He iin = 4–5 (10 124 Å) and n = 4–6 (6560 Å) Line Complexes in a Low-Temperature Hollow Cathode*

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Abstract
The He II n = 4–5 (10 124Å) and n=4–6 (6560 Å) line complexes, not previously studied at high resolution, have been excited in a liquid-nitrogen-cooled hollow cathode and observed with a double Fabry-Perot spectrometer. Relative positions, relative intensities, and widths of the fine-structure components have been determined by computer analysis of the digitally recorded spectra of both 3He and 4He. The relative positions of the best-resolved components have been determined to ±0.002 cm-1 and show agreement with theoretical fine structures and isotope shifts. The accuracy of the position measurements is limited by the highly blended nature of the transitions, there being 19 broadened components over a 1.1-cm-1 range. The observed relative intensities approximated statistical relative intensities except for components arising from S and P states, which were three to five times more intense than the theoretical values. The measured widths of the ion lines are roughly 1.15 times those observed for He I lines. The intensity and width results are consistent with observations previously reported for the He II n = 3–4 (4686 Å) transition and support the conclusions on the excitation mechanisms that were inferred from a study of that transition.