- forbidden lines
- forbidden lines,Physics. spectral lines of radiation produced by changes in energy level that occur within an atom only when the interval between atomic collisions is exceptionally long: »
They are the so-called forbidden lines—colors which an atom is extremely reluctant to radiate and will not radiate at all unless left undisturbed by collisions for seconds or minutes at a time (Armin J. Deutsch).
Useful english dictionary. 2012.
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