REEXAMINATION OF THE HE(-)1S2P(2)P-4(E) SHAPE RESONANCE - DETAILS OF ITS PROPERTIES AND A PRECISE ELECTRON-AFFINITY FOR HE 2S-3

The huge He- 4P(e) shape resonance was reexamined in photodetachment u sing a titanium:sapphire laser tuned over the energy range 9740-10 300 cm-1. This range covered well below the He (2(3)P) threshold and incl uded the entire resonance region. The uncertainties in the earlier dat a [Peterson et al., Phys. Rev. Lett. 55, 692 (1985)] were greatly redu ced. The new (old) experimental value for the electron affinity of He (2(3)S) is 77.67+/-0.12 meV 77.6+/-1.0 meV), in fair agreement with th e most accurate theoretical value, 77.51+/-0.04 meV, of Bunge and Bung e [Phys. Rev. A 30, 2179 (1984)]. This resonance lies 10.80+/-0.07 meV above the He 2(3)P threshold, and has a decay width of GAMMA = 7.16+/ -0.07 meV. The ratio of the cross section at resonance to the continuu m at the threshold is sigma(R)/sigma0 = 89+/-5. This study provides by far the most detailed experimental view of an electronic shape resona nce.