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The anticipated terms of multiplicity 11, "P"D"F (combining with a higher "D°), and also slightly higher 9D° and 9S° terms have been identified in Gd i. From these, the first ionization potential is found to be 6.16 volts. AIbertson's conclusion that the lowest configuration in Gd U is 4f76s5d'°D° is confirmed. The terms 4f76s2 8S° probably lies about 0.5 volts higher
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Henry Norris Russell (1942) studied this question.
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