The structure of the spectrum of ionised nitrogen

Abstract

In accordance with recent developments in the analysis of spectra, it is to be expected that, while the neutral atom of nitrogen (N·I) will yield a spectrum derived from systems of terms of even multiplicity, the spectrum of ionised nitrogen (N II or N + ) will be constituted from terms of odd multiplicity. The spectrum of doubly-ionised nitrogen (N III or N ++ ) is similarly expected to be formed from terms of even multiplicity. The probable existence of the three types of line spectra representing N I, N II and N III has already been pointed out, but few details regarding the regularities in the respective spectra have hitherto been available. A spectrum which probably represents N I has been described by Stark and Hardtke, but accurate measurements of the lines do not appear to have been made; Bowen and Millikan, however, have attributed to N I two well-known pairs of lines in the Schumann region at λλ 1745·3, 1742·7, 1494·8 and 1492·8. implying even multiplicity of the terms involved.