THE SPECTRUM OF TREBLY IONIZED THORIUM

Abstract

An analysis of the spectrum of Th IV is given which includes practically all the stronger known lines of thorium which can be attributed to the trebly ionized atom. This spectrum all lies on the short wave-length side of 2350 Å, with the exception of one line, 7S—7P, which falls at λ2694.00 Å. Most of the lines of the spectrum above 2000 Å are quite intense in the spark in air, but do not appear at all in the arc and are definitely enhanced in the vacuum spark. The separation of the deepest 7P terms has the relatively enormous value of 12818 cm−1. The terms 7P, 6D, 7D, 8D, 7S, 8S, 9S, 5F and 5G have been found. The ionization potential of Th+++ is approximately 29.4 volts.