Definition: | spectral line that is the result of direct transition from an excited energy level to the ground level, or vice versa, without going through intermediate levels EXAMPLE For mercury, the resonance line is at λ = 253,7 nm and for sodium it is at λ = 589,6 nm. Note 1 to entry: This entry was numbered 845-04-35 in IEC 60050-845:1987.
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