Energiatason

Energiatason, or energy level, is a discrete value of energy that a quantum system can possess. In quantum mechanics, many systems, including atoms and molecules, have quantized energy levels rather than a continuous range. Each level is associated with a set of quantum numbers, and in atoms these levels are often described as shells and subshells. Levels can be degenerate, meaning several quantum states share the same energy.

Transitions between energy levels involve exchange of energy with light or other fields. The energy difference ΔE between two levels corresponds to the energy of a photon absorbed or emitted, with ΔE = hν, where ν is the frequency of the photon. Selection rules determine which transitions are allowed. Emission and absorption spectra reveal the arrangement of energy levels and provide a sensitive probe of the structure of atoms and molecules.

Models of energy levels vary in complexity. For the hydrogen atom, energy levels follow E_n = -13.6 eV / n^2. In multi-electron atoms the picture is more complex due to electron–electron interactions, shielding, and relativistic effects. External fields can lift degeneracy and shift levels through Stark or Zeeman effects, producing fine structure or spectral line splitting.

Population of energy levels depends on temperature and excitation. The Boltzmann distribution describes relative occupancies; at room temperature higher levels are sparsely populated, while intense excitation can populate them. Bound levels terminate at the ionization threshold, above which states merge into a continuum.

Applications of energy levels include spectroscopy for element identification, lasers and masers that rely on stimulated transitions, semiconductor devices and quantum dots with engineered gaps, and atomic clocks that use precise energy differences for timekeeping.