Excited state

An excited state is a state of a system with greater energy than its ground state. It can arise when the system absorbs energy and often decays by releasing energy.

Ground state: The lowest-energy state available to a system under specified conditions. It is the reference state whose energy an excited state exceeds.
Energy level: A permitted value of energy for a quantum system. An excited state occupies an energy level above the ground level.
Absorption spectroscopy: A method that identifies matter by measuring which frequencies it absorbs. Its spectral lines reveal energy gaps leading to excited states.
Vibrational excitation: A molecular state with increased vibrational energy relative to its vibrational ground level. It raises molecular energy through nuclear motion rather than electronic promotion.
Energy transfer: The movement of energy from one part of a system to another without necessarily transferring matter. Excitations can migrate between molecules or regions before they decay.
Quantum transition: A change between allowed quantum states, often involving absorption or emission of energy. Excitation moves a system between energy levels through a quantum transition.
Quantum number: A value that labels a quantized property of a quantum state. Quantum numbers distinguish excited configurations from the ground-state configuration.
Fluorescence: Light emission following absorption, typically from an excited electronic state. Fluorescence records radiative relaxation from excited states.
Rotational excitation: A molecular state with increased rotational energy relative to its rotational ground level. It is a distinct, typically lower-energy form of molecular excitation.
Excited-state dynamics: The time-dependent evolution of a system after it enters an excited state. Its measurements reveal competing relaxation and reaction pathways.

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