Cross section and angular distribution for the photodetachment of He^-(1s2s2p ⁴P^o) below the He(n=4) threshold

A detailed investigation is performed for the photodetachment cross section of the He^- from the metastable 1s2s2p ⁴P^o state, with photon energy up to 4 eV, which covers the whole energy region up to the He(n=4) (n is the principal quantum number for the outer electron) threshold. The B-spline basis and inverse iteration approach is employed to solve the multichannel process. In contrast to other earlier theoretical calculations, in addition to the 1s2p^{2 4}P sharp resonance, we also find 1s3p^{2 4}P, 1s3p4p ⁴P, 1s4p^{2 4}P, 1s4p5p ⁴P, and 1s3s4s ⁴S Feshbach resonances in this energy region. Two Cooper minima are found in the 1s2p(³P^o)kp ⁴P channel at the energies of 2.83 and 3.25 eV. The angular distribution of the photoelectrons is also studied; the asymmetry parameter β with respect to the He(2,³P^o) target is quite different from earlier predictions due to the Feshbach resonances in the photodetachment to the final ⁴P state. © 1996 The American Physical Society.