Elektronentransities

Elektronentransities, often called electronic transitions, describe changes in the electronic structure of atoms, ions, or molecules as electrons move between quantized energy levels. These transitions involve the absorption or emission of photons and are observed as characteristic features in spectra across the electromagnetic range, from ultraviolet to infrared and, in many cases, as X-ray transitions involving core electrons.

In atoms, energy levels are discrete and transitions follow selection rules. Electric dipole-allowed transitions require a change in orbital angular momentum (Δl = ±1) and a change in parity, with spin nearly conserved. Absorption promotes an electron to a higher state; emission returns it to a lower state. The energy difference ΔE equals hν = hc/λ, producing line spectra whose positions reveal the level structure of the atom.

In molecules and solids, electronic transitions are often accompanied by changes in vibrational and rotational states, yielding bands rather than sharp lines. The Franck-Condon principle explains that electronic transitions occur on timescales much shorter than nuclear motion, making transitions approximately vertical on potential-energy surfaces. Transition intensities depend on the transition dipole moment and the overlap of vibrational wavefunctions.

Non-radiative electronic transitions include internal conversion and intersystem crossing, where energy is dissipated as vibrational heat or transferred to different spin states rather than emitted as photons. The balance between radiative and non-radiative channels determines excited-state lifetimes and quantum yields.

Applications span spectroscopy, chemical analysis, and material science, including lasers, light-emitting devices, fluorescent probes, and solar-energy technologies. Understanding electronic transitions is essential for interpreting spectra and for designing systems that control light absorption and emission.