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Wavefunctions obtained with the relativistic CI method are used to determine in a fully ab initio manner, the electronic part of a two-photon non-resonant transition between the Is²2s²2p²³P₀ and ls²2p⁴³P₂ even levels of O III. The levels ls²2s2p³ (³D_l, ³P_l, ³S_l, ¹P_l), ls²2s²2p3s (³P_l^lP_l), and ls²2s²2p3d (³D_l, ³P_l, ¹P_l) J=1 have been used in the truncated summation method. The photon field is expanded in terms of multipoles and matrix elements in the Coulomb gauge depend negligibly on the omega values of the beams involved in the transition. Results reported may be used in the calculation of two-photon absorption cross sections thus demonstrating the relevance of the relativistic CI method in laser-assisted spectroscopic studies of atoms and ions.

The authors consider harmonic generation by one-dimensional systems and low frequency periodic electric fields; they provide a detailed description of the classical dynamics of an arbitrary system, but treat the quantal dynamics in less detail indicating only those regions where the two dynamics either produce similar results or are quite different. They express the Hamiltonian in an adiabatic representation, which has the correct limit as the field frequency tends to zero; this enables them to show that for very low frequency fields the classical and quantal mechanisms of harmonic generation are the same. The non-adiabatic correction terms may manifest themselves in different manners according to whether a classical or a quantal description is used. In the classical case, they provide an analytic description of the motion of an arbitrary system valid for fields which do not ionize the system and have sufficiently low frequency; they apply this theory to a one-dimensional hydrogen atom. In the quantal case we provide a more approximate description. The results, which are system independent, explain many features of extant numerical calculations.

Photoabsorption cross sections in the autoionization regions of Ar, Kr and Xe have been measured with resolutions of 0.0045 AA for Ar and 0.0074 AA for Kr and Xe using a high-resolution spectrometer installed in the Photon Factory, a 2.5 GeV synchrotron radiation facility in Tsukuba. The cross sections are parametrized with the aid of a lineshape formula which is based on the multichannel quantum-defect theory and has a form analogous to Fano's resonance formula. These are compared in detail with other experimental data and theoretical predictions available in the literature.

The Lyman and Balmer series in hydrogen-like Dy⁶⁵⁺, along with radiative electron capture (REC) into bare Dy⁶⁶⁺, have been observed. The X-ray spectra were measured in coincidence with one-electron capture in a beam of 292 MeV amu^-1 Dy⁶⁶⁺ stored in the ESR storage ring and interacting with an internal argon gas target. The REC line profile was studied in detail and was in good agreement with theory, thus suggesting additional possibilities for spectroscopy.

In calculations of the laser-induced ionization of uranium atoms it is necessary to average over all phases in the initial multicomponent wavefunction, the components corresponding to the initially occupied hyperfine states. In practice, however, the results of such a mixed state calculation differ only slightly from those obtained from a pure state calculation, which uses a single initial state with a random choice of phases. The statistical properties of multidimensional unit vectors are used to explain this observation, suggesting that the system is sufficiently complicated that the properties of the eigenvectors of the Hamiltonian are well represented by an ensemble over all possible orientations. This supports the use of pure state calculations in laser isotope separation studies, which offer a large reduction in the necessary computational effort.

Cross sections for electron capture from the n=2 excited states of atomic hydrogen in collisions with protons and alpha particles are calculated using the semiclassical close-coupling method where the time-dependent wavefunction is expanded in terms of travelling atomic orbitals on each collision centre. The results are compared with existing close-coupling calculations in which molecular orbital expansions were used. The dependence of the total and partial electron capture cross sections on the alignment of the initial excited 2p states is examined.

Based on a Dirac R-matrix (close-coupling) calculation, the authors present results for various spin-polarization parameters for elastic and inelastic scattering of slow (E_kin<or approximately=2 eV) polarized electrons from unpolarized and polarized neutral Cs atoms in their ground state. Their results allow for a quantitative estimate of the importance of relativistic effects, and their calculated parameters clearly deviate from predictions obtained by just jj-recoupling the results of a non-relativistic calculation.