Double electron capture theories: Second order contributions

The study of multielectron processes, where two or more electrons are invol ved, has usually been carried out by using independent electron approximati ons associated with one electron processes. In our studies of the double el ectron capture reaction at intermediate and high collision energies by impa ct of bare heavy ions on He(1s(2)) targets, an independent electron treatme nt of distorted wave approximations has been employed but also four body mo dels were used, in order to shed some light on the role played by the elect ronic correlation during the collision. Theoretical results using distorted wave approximations calculated in both frameworks am presented and compare d with experimental data available at present and with other theoretical ca lculations.