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A new cascade-decoupling technique has been used to measure hyperfine intervals (in MHz) of the following excited S states of alkali-metal atoms: K³⁹(6²S1/2)46±2; K⁴¹(6²S1/2)26±2; Rb⁸⁵(7²S1/2)270±10; Rb⁸⁵(8²S1/2)135±15; Rb⁸⁷(7²S1/2)565±60; Rb⁸⁷(8²S1/2)290±20; Cs¹³³(8²S1/2)680±120; and Cs¹³³(9²S1/2)405±30.
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Gupta et al. (1972) studied this question.
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