Excitation of Atoms

The addition of a discrete amount of energy (called excitation energy) to an atom or a molecule that results in its alteration, ordinarily from the condition of lowest energy (ground state) to one of higher energy (excited state). Excitation may result from absorption of a photon or from collision with energetic electrons. The life span of an excited electron is usually very short; when the electron returns to its ground state or to a state of lower energy, energy is released.