An Etymological Dictionary of Astronomy and Astrophysics
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Any of the several discrete states of energy which a particle, atom, or molecule can adopt under conditions where the possible values are restricted by quantum mechanical laws.

→ energy; → level.

The splitting of a single atomic level into a group of closely spaced levels when the substance producing the single line is subjected to a uniform magnetic field. → Zeeman effect; → Stark effect.

→ spliting; → energy level.