A state of a system when it has an energy level permitted by quantum mechanics. Transitions from one stationary state to another can only occur by the emission or absorption of an appropriate quanta of energy (e.g. in the form of photons).
Chemistry
A state of a system when it has an energy level permitted by quantum mechanics. Transitions from one stationary state to another can occur by the emission or absorption of an appropriate quanta of energy (e.g. in the form of photons).
Electronics and Electrical Engineering
The state of an atom or other system that in the quantum theory or quantum mechanics is described by a given set of quantum numbers. Each of the various energy states that may be assumed by an atom is a stationary state of that atom.