First Spark Spectrum of Thorium—Classification and Zeeman Effect Data of Th II

Five sets of exposures to the thorium arc in silver, burning in a Bitter electromagnet at fields up to 93,000 oersteds, have given resolved Zeeman patterns for more than 800 lines of Th II. Data obtained from these plates, measured with an automatic comparator and used in connection with improved wave-length measurements, have made possible classification of 1091 lines of Th II as arising from 219 levels. These levels belong to two groups of terms between which no combinations have been found. Group A contains even terms arising from d2s (with a4F112 lying lowest), from d3, and from ds2, and odd terms from d2p, dsp, and fds. About half of all terms expected from these configurations have lceen identified. Group B contains odd terms expected from fs2 (with a2F°212 lying lowest), and fds, and even terms from fsp and fdp. g values are given for all levels, in many cases to within 0.002 unit, which makes available a large amount of fairly exact experimental data for evaluation of perturbations. Partial tests of the g sum rule show good agreement with theory, though all terms are not yet available for inclusion. Perturbations of even those terms which lie low are rather large.