Quasi-projection-operator calculation of inelastic resonances inHe−and Li

Feshbach resonances of electrons incident on He and ${\mathrm{Li}}^{+}$ are calculated below the $3{}_{}{}^3{}_{}{}^{}S$ target threshold by means of the inelastic quasi-projection-operator technique of Temkin and Bhatia. A configuration-interaction-type wave function is employed with up to 46 configurations. The calculations reveal, with reasonable accuracy, all presently observed Feshbach resonances. The method does not reveal shape resonances, but, for isoelectronic systems with greater nuclear charge, it is argued that shape resonances should become less important. This is already apparent in the case of Li, for which the authors calculate the known resonances and also predict higher resonances for which there are as yet no experimental data.