On the Spectra of Hg II and Hg III

The structure of many lines of ionized mercury in the region 6000-2200A has been investigated by means of apparatus of high resolving power. Many of the lines have been found to possess complex structure. The structures found are presented in the form of graphs, in which approximate distances and intensities of components are given. In a few cases more exact values of the distances are indicated. From the data collected in Table I and Fig. 2 the isotope shifts in 47 energy levels of Hg II and the hyperfine structure splittings in ten of them have been roughly determined (Table II). The isotope shift and hyperfine splitting are very small for levels of the configuration $5d^{10}\mathrm{nx}$ (where $\mathrm{nx}$ designates electronic orbits higher than $6s$), and quite considerable for levels of the type $5d^{9}6snx$. In the latter case shifts of about 0.3 ${\mathrm{cm}}^{-1\mathrm{}}$ between consecutive even isotopes Hg 200 and 202, and hyperfine splittings amounting to from 0.4 to 1.3 ${\mathrm{cm}}^{-1\mathrm{}}$, have been found. Some levels of the configuration $5d^{10}\mathrm{nx}$ show perturbation in the isotope shift; the levels ${15\mathrm{°}}_{3/2}$ and ${25\mathrm{°}}_{5/2}$ reveal a strong perturbation of the same kind. The data collected in Table III, Fig. 3, and Fig. 4 present the results in the cases of lines for which no correct classification seems to be known. They belong, mostly at least, to Hg II, and possibly some of them to Hg III. The results show the necessity of rejecting the existing classification of these lines (Hg II and Hg III) and some of the term values previously given for Hg II by Paschen, by Naude, and by Venkatesachar and Subbaraya. A discussion taking into account also the conditions of excitation reveals many doubts about the correctness of an extension of the analysis of the spectrum of Hg III reported by Johns. The most interesting among the lines studied are lines with isotope shifts which are the highest among all known spectra, and most of which at the same time possess no observable hyperfine structure. Since a discussion shows that probably they do not belong to Hg III, their presence furnishes evidence for the existence of two previously unknown sets of levels in Hg II, belonging to configurations $5d^{8}6s^2\mathrm{nx}$ and $5d^9\mathrm{nx}{n}^{\prime }{x}^{\prime }$, by which the presence of a considerable number of hitherto unclassified lines can be understood.