Two-electron photoionization processes in He@C60 using the R-matrix with pseudostates and time-dependent close-coupling methods

The R-matrix with pseudostates method is applied to the case of two-electron excitation and ionization processes in He@C-60. A finite spherical-well potential, which simulates the effect of the fullerene enclosing cage, is incorporated into the Hamiltonian using a modified R-matrix method, as recently applied to similar single photoionization studies of Xe@C-60 and Ca@C-60. Comparison is made with time-dependent close-coupling results for two-electron processes in He and He@C-60, and excellent agreement is found in the respective descriptions of confinement resonances. Earlier findings are confirmed that the cage potential causes a redistribution between the n = 2 and n = 3 photoionization-excitation cross sections. The R-matrix with pseudostates method, in particular, is well-suited for treating atomic Feshbach resonances and studying multi-electron systems.