A simple method to extract resonance information from the Harris energy eigenvalues and eigenvectors

Within the framework of the J-matrix method of scattering, a given multichannel potential is modelled by its restriction on a subspace spanned by a certain set of L² functions. The scattering S-matrix is found exactly for this model potential at the Harris eigenvalues which result from the diagonalization of the scattering Hamiltonian in the same subspace. These values are then analytically continued in the complex energy plane. The poles of the S-matrix are then identified with the complex resonance energies. The associated widths for each resonance are then extracted from the residues of the S-matrix elements at the designated energy.