Series of Doubly Excited Quartet States of He

Twelve previously unobserved Feshbach resonances associated with the autodetaching decay of doubly excited states of He{sup {minus}} have been observed in the process of photodetachment. Seven resonant states of {sup 4}P symmetry and one of {sup 4}S symmetry have been identified in the energy range which encompasses the He(n=4,thinsp5) thresholds. Their measured energies and widths agree with recent calculations. A functional form representing the energies of members of the {sup 4}P series has been derived. This form is fundamentally different from the Rydberg-dipole formula that describes doubly excited states of H{sup {minus}} . {copyright} {ital 1998} {ital The American Physical Society }