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Intersystem combination lines of the third spectrum of argon have been discovered in the extreme ultraviolet. The lines are listed and the singlet term values previously published are revised to conform to the same basis as that of the triplet terms. Wave-lengths of the "forbidden" lines of this stage of ionization of argon have been calculated. One of them is in close agreement with a nebular line at λ7135.6.
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J. C. Boyce (1936) studied this question.
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