trekroppsrecombination

Trekroppsrecombination, or three-body recombination, is a collisional process in which a free electron recombines with a positively charged ion in the presence of a third particle that carries away the excess energy and momentum. The third body is typically another free electron or a neutral atom in the gas. The result is a bound electronic state of the ion.

During the interaction, the captured electron transitions into a bound state while the third particle takes away the energy. Because momentum and energy must be conserved among three bodies, the process is enhanced only when particle densities are high and frequent collisions occur. Unlike radiative recombination, three-body recombination does not require photon emission; energy transfer to the third body suffices.

Temperature and density control its rate. The overall rate scales with the densities of the participating species (roughly with the product n_e^2 n_i in a quasi-neutral plasma) and is strongly temperature dependent, typically increasing at lower temperatures. As a result, three-body recombination dominates the ionization balance only in sufficiently dense, relatively cool plasmas.

Applications include laboratory plasmas, stellar interiors, and inertial confinement fusion research, where accurate modeling of recombination requires including three-body processes. It is a complement to radiative (two-body) recombination, which dominates at lower densities.

See also: three-body recombination in plasma physics; radiative recombination; ionization balance.