The Coulomb integrals and the diffraction model of transfer reactions

The resonating group interaction of three clusters, in the single channel no-distortion approximation, is split into a leading part and a residual part. In norm kernel eigenstate representation, the leading part exhibits a peculiar, fish bone like symmetry. An off-shell transformation, which leads to an energy-independent interaction, also reduces the strength of the three-body Pauli potential. The smallness of this potential is related to the possibility of interpreting cluster relative motion wave functions as probability density amplitudes. Neglecting all residual interactions and introducing, instead, fitting parameters into the two-cluster direct interactions leads to a three-cluster optical model. In this model the on-shell behaviour of two-cluster interactions is determined by experimental data, while their off-shell behaviour, as well as the three-cluster Pauli potential, are determined by the Pauli principle.