An experimental and theoretical study of ground-state photoionization of neon is presented in the photon energy range between 44 and 53 eV. This portion of the spectrum is characterized by a singly excited Rydberg series 2s2p 6 np, and by overlapping doubly excited Rydberg series 2s 2 2p 4 3snp and 2s 2 2p 4 3pnl (lϭs,d).With the use of synchrotron radiation of Х3 meV spectral resolution, numerous hitherto unobserved resonances were resolved, including some which exhibit relativistic effects. To identify resonances observed here and in earlier works, we employed numerical calculations, which combine the eigenchannel R-matrix method, multichannel quantum defect theory, and the recoupling frame transformation. These nearly ab initio methods account for most of the observed features in the spectrum, including a class of spin-induced relativistic effects.

We develop a theoretical description of the anisotropic interaction between a Rydberg electron and an ionic core. An adiabatic formulation expresses the anisotropic nature of the interaction through angular-momentum operators of the core and the Rydberg electron. Terms with odd tensorial structure, such as a vector hyperpolarization proportional to L ជ c •l ជ , emerge in the long-range potential. Computed energies of neon nϭ10 Rydberg states are compared with recent experimental measurements. The vector term improves agreement between theory and experiment. The vector hyperpolarizability is calculated explicitly, along with some standard polarizabilities of Ne ϩ .

A non-variational Galerkin method, completely based on B-spline methods is introduced and applied to calculations of resonance positions and widths in H- and He. The results agree very well with other theories and experiments. Photodetachment in H- and photoionization of He are also considered.