THEORY AND COMPUTATION OF TRIPLY EXCITED RESONANCES - APPLICATION TO STATES OF HE-

Autoionizing multiply excited states offer unusual challenges to the t heory of electronic structure and spectra because of the presence of s trong electron correlations, of their occasional weak binding, of thei r proximity to more than one threshold, and of their degeneracy with m any continua. Here we discuss a theory that addresses these difficulti es in conjunction with the computation of their wave functions and int rinsic properties. Emphasis is given on the justification of the possi ble presence of self-consistently obtained open-channel-like (OCL) cor relating configurations in the square-integrable representation of suc h states and on their effect on the energy E and the width GAMMA. Appl ication of the theory has allowed the prediction of two hitherto unkno wn He- triply excited resonances, the 2s2p2 2P (E=59.71 eV, above the He ground state, GAMMA=79 meV) and the 2p3 2D(o) (E=59.46 eV, GAMMA=28 2 meV) (1 a.u.=27.2116 eV). These resonances are above the singly exci ted states of He and are embedded in its doubly excited spectrum. The relatively broad 2p3 2D(o) state interacts strongly with the He 2s2p P -3(o) epsilond continuum. The effect of this interaction has been stud ied in terms of the coupling with fixed core scattering states as well as with a self-consistently computed OCL bound configuration. The pos ition of the He- 2p3 2D(o) resonance is below that of the He 2p2 1D au toionizing state at 59.91 eV and of the He 2p2 3P bound state at 59.68 eV. The partial decay widths to the three important open channels are gamma(2s2p P-3(o))=252 meV, gamma(1s2p P-3(o))=21 meV, gamma(1s2p P-1 (o)) = 9 meV. The final core states are also represented by correlated (multiconfigurational Hartree-Fock) functions. The 2s2p2 2P state cou ples to four neighboring He thresholds, the 2s2p P-3(o), 2p2 3P, 1D, a nd 2s2p P-1(o). It is above the He 2s2p P-3(o) threshold at 58.31 eV, with respect to which it is a valence shape resonance, and below the H e 2p2 1D and 2s2p P-1(o) autoionizing states. In the limit of an exact energy calculation, we suggest that its position would also come belo w that of the 2p2 3P state, which it overlaps. Its partial widths are gamma(2s2p p-3(o))=60 meV, gamma(1s2p P-3(o))=9 meV, gamma(1s2p P-1(o) )=10 meV. The present results, considered together with published ones on other n=2 intrashell states, show that the recently measured [R. N . Gosselin and P. Marmet, Phys. Rev. A 41, 1335 (1990)] closely lying structures at 58.415 and 58.48 eV cannot correspond to the He- 2p3 S-4 (o) and 2D(o) states, as these authors proposed.