QuadrupolÜbergänge

QuadrupolÜbergänge are a type of electromagnetic transition that can occur within atoms and molecules. Unlike electric dipole transitions, which are the most common type of radiative transition, quadrupolÜbergänge involve a change in the quadrupole moment of the system. This means that the spatial distribution of charge within the atom or molecule must change in a way that can be described by a quadrupole operator. QuadrupolÜbergänge are generally much weaker than electric dipole transitions, meaning they occur with a lower probability and are less likely to be observed.

The selection rules for quadrupolÜbergänge are different from those for dipole transitions. For electric quadrupole transitions, the change in the total angular momentum quantum number J must satisfy ΔJ = 0, ±1, ±2, but J=0 to J=0 transitions are forbidden. The parity of the state must also change. Magnetic quadrupole transitions have different selection rules, typically involving a change in J of ΔJ = 0, ±1, ±2, and they do not require a change in parity.

Due to their weaker nature, quadrupolÜbergänge are often observed in situations where dipole transitions are forbidden or strongly suppressed. This can occur in certain molecular spectroscopy experiments or in the study of specific atomic energy levels. While less common, their observation can provide valuable information about the electronic structure and symmetry of the participating states. The probability of a quadrupolÜbergang is proportional to the square of the matrix element of the quadrupole operator between the initial and final states.