We present a multichannel reaction matrix theory for perturbed discrete and continuous spectra, using Hartree-Fock (HF) or MCHF-based configuration-interaction (CI) wavefunctions, in the Breit-Pauli approximation. The function space is divided into two parts, P and Q, computed separately for different configurations in a state-specific quasi-relativistic framework. The Q functions are correlated low-lying, inner-hole and valence-excited states, whilst the P functions are symmetry-adapted products of correlated (N-1) electron cores with Rydberg and scattering HF or MCHF orbitals. Energy dependent, smooth reaction matrices are found, from which the total wavefunctions are constructed. Calculations very close to and on threshold present no problems. Application is made to the Al 2D spectrum, for which quantum defects, oscillator strengths and fine structure (FS) are calculated. The latter was calculated and measured by Buurman and coworkers (1989-90), who disagreed with earlier theoretical results of Weiss and others (1974). Our results do not confirm their conclusion. Furthermore, the treatment of FS and the good agreement with experiment show that, the inclusion of coupling of '3s3p2' 2D and '3s3pnp' 2D states is crucial. The contribution of other nonrelativistic terms is insignificant.

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We present a many-electron, many-photon (MEMP) nonperturbative theory of nonlinear static and dynamic polarizabilities of polyelectronic atoms and molecules. The time-dependent, dynamic polarization is treated as a frequency-dependent problem with the Floquet assumption that the computed quantities are averaged over a cycle.The MEMP theory defines a non-Hermitian problem whose efficient solution yields a complex eigenvalue to all orders in the interelectronic and the electron ac or dc field interactions. When the real part is subtracted from the unperturbed energy of the free state, we are left with the frequency-dependent total energy shift A(w). This is then fitted to a polynomial expansion whose coefficients are the required polarizabilities representing the induced polarization averaged over a cycle. Results are given for the a, a(w), and y, y(w) of H and of Li-. For Li-, only a had been computed earlier by many-electron approaches. The dynamic a(w) was computed before in a quasi-classical approximation with a simple wave function. Comparison shows a qualitative agreement but not a quantitative one.

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Calculations incorporating the effects of electron correlation on the Auger energies and widths of the neon 1s2(2s2p5)3,1P03p2S states have given results in agreement with the recent measurements of Pahler et al. The Ne+ 1s22s2p5 1P03p2S autoionizing state is above the Ne2+ 1s22s2p5 3P0 threshold and, using the theoretical Auger electron energy, its decay width to this channel is computed to be 0.48 eV. At the Hartree-Fock level this quantity is equal to 0.280 eV. The partial width of the 1P03p 2S state to the Ne2+ 2s22p4 1D channel is essentially zero while that to the Ne2+ 2s22p4 1S channel is 0.028 eV.