The Classification of the Spectrum of Singly Ionized Tin. Sn II

The spectrum of Sn II, as excited in a hollow cathode discharge in helium, has been photographed from 800A to 10,000A. Some 70 new lines have been classified and 28 new levels established. A few changes have been made in the levels and classifications previously made by Green and Loring, Narayan, and Lang. The $5s^2\mathrm{ms}$, $-mp$, $-md$ and $-mf$ series have been extended, and the ${}_{}{}^2{}_{}{}^{}F$ levels have been resolved for the first time. Six members of the $5s^2\mathrm{mg}$ ${}_{}{}^2{}_{}{}^{}G$ series have been located and used to make a new determination of the ionization potential of Sn II as 118,017±3 ${\mathrm{cm}}^{-1\mathrm{}}$. The classification has been checked by series relations, Zeeman patterns, and by comparison with the isoelectronic spectra In I and Sb III. Irregularities in the ${}_{}{}^2{}_{}{}^{}S$ and ${}_{}{}^2{}_{}{}^{}D$ terms are explained qualitatively by consideration of interactions with perturbing terms from the configuration $s{p}^2$.