excitation energy

atomic physics

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June 26, 2026

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In atomic physics, excitation energy refers to the discrete amount of energy needed to move a system, such as an atom or molecule, from its lowest energy state (ground state) to a higher energy state (excited state). This energy is not continuous; only specific amounts can be absorbed. For instance, a hydrogen atom requires 10.2 electron volts to move an electron from its ground state to the first excited state.1

When an atom is in an excited state, it can return to its ground state by emitting this stored energy, often as visible light or gamma radiation. This process is fundamental to how matter absorbs energy, such as light, and can be heated or ionized. Excited states are distinct energy levels within an atom, and transitions between these levels produce spectral lines.123

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excitation
…discrete amount of energy (called excitation energy) to a system—such as an atomic nucleus, 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).
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…discrete amount of energy (called excitation energy) to a system—such as an atomic nucleus, 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).
Read More