Electronic transition

An electronic transition is a change in an atom or ion from one quantized electronic energy level to another, often through absorption or emission of a photon.

Photon absorption: The transfer of a photon's energy to matter, often raising an electron to a higher energy level. Absorption promotes an electron when the photon energy matches the difference between two levels.
Atomic orbital: A quantum state describing the spatial distribution and other properties of an electron in an atom. Atomic orbitals label many of the states connected by atomic transitions.
Atomic spectroscopy: The study of matter through its interaction with electromagnetic radiation at atomic wavelengths. Atomic spectra reveal electronic transition energies and characteristic line patterns.
Vibrational transition: A change between quantized vibrational states of a molecule. Vibrational transitions change nuclear motion states rather than electronic states.
Photon emission: The release of a photon when matter loses energy, including when an electron falls to a lower energy level. Emission accompanies downward transitions whose energy gaps set the emitted photon frequencies.
Quantum number: A number that specifies a quantized property of a quantum state, such as energy or angular momentum. Quantum numbers determine the states and symmetry changes used to classify transitions.
Absorption spectrum: A record of wavelengths removed from a source spectrum by a material. Absorption features mark photon energies that drive upward electronic transitions.
Rotational transition: A change between quantized rotational states of a molecule or other system. Rotational transitions alter angular motion without changing the electronic state.
Selection rule: A constraint specifying which transitions between quantum states are allowed or forbidden under a given interaction. Selection rules identify transitions that can produce observable spectral lines.
Energy level: A discrete allowed energy value of a quantum system. Transitions connect the quantized energies whose differences govern exchanged energy.

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