T. N. Chang

Oscillator strengths for the bound-bound transitions in beryllium and magnesium

Abstract We present theoretical oscillator strengths for the bound-bound transitions between selected 1,3 S , 1,3 P , 1,3 D , and 1,3 F states of beryllium and magnesium atoms, determined from a simple configuration-interaction calculational procedure using a finite basis constructed from B splines. A detailed qualitative discussion is also presented on the effect of configuration interaction on the oscillator strengths for various groups of transitions.

Photoionization of the Inner‐Shell Electron under Changing Outer‐Shell Electronic Environment in Alkali Atoms

Recent experimental study at LURE on the photoelectron spectrum of the 2p‐subshell of sodium atom with its valence electron excited by laser has made it possible to examine in detail the photoionization of the inner‐shell electron under changing outer‐shell electronic environment. In this paper, we report the result of a comprehensive theoretical study of this atomic process for alkali atoms with the valence electron at various stages of excitation. The contribution from important many‐body interactions to the photoionization cross section is examined. The calculated cross section and the angular distribution of the ejected photoelectron are presented.

Energy levels and transition probabilities of bound excited states of Be-like N IV

Abstract We present the theoretical energy values and the transition probabilities for a series of singly and doubly excited states below the first ionization threshold of the Be-like N IV ion calculated in a simple nonrelativistic configuration-interaction procedure using a finite L 2 -basis set constructed from B splines. Our calculated energies and radiative lifetimes are found to agree closely with all available observed data.

Column density and temperature effects on narrow resonance structures in atomic photoionization and photoabsorption

We consider a formation of the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase in a quasi-onedimensional (Q1D) conductor in a magnetic field, parallel to its conducting chains, where we take into account both the paramagnetic spin-splitting and orbital destructive effects against superconductivity. We show that, due to a relative weakness of the orbital effects in a Q1D case, the LOFF phase appears in (TMTSF)2ClO4 superconductor for real values of its Q1D band parameters. We compare our theoretical calculations with the recent experimental data by Y. Maeno’s group [S. Yonezawa et al., Phys. Rev. Lett. 100, 117002 (2008)] and show that there is a good qualitative and quantitative agreement between the theory and experimental data.

Spin-mixed doubly excited resonances in Ca and Sr spectra

We present a joint theoretical and experimental investigation to demonstrate explicitly how the combined spin-dependent interaction and the configuration interaction may affect the mixing of different spin states along various doubly excited autoionization series for Ca and Sr as energy increases across several ionization thresholds. In particular, our study has identified the inversion of energy levels between members of a number of multiplets, i.e., in contrast to the Hunds rules, due to the presence of perturber from other overlapping resonance series. We are also able to demonstrate the beginning of the breakdown of the LS coupling for resonance series corresponding to electron configurations with higher orbital angular momenta and those above the third ionization threshold.

B-spline-based complex-rotation method with spin-dependent interaction

We present a B-spline-based complex-rotation (BSCR) method with spin-dependent interaction for the study of atomic photoionization leading to multiple ionization channels dominated by doubly excited resonances for two-electron and divalent atoms. The degree of mixing between different spin states and between the bound and continuum components of the state function of the resonance state can be easily identified in the BSCR method. Its application to Mg photoionization gives good agreement with observed singlet-triplet mixed Mg spectra.

Core-excitation effects on atomic transitions

By including explicitly the electronic configurations with three simultaneously excited electronic orbitals, we have successfully extended the BSCI (B-spline based configuration interaction) method to estimate directly the effects of inner shell core-excitation to atomic transitions. In particular, we are able to carry out detailed ab initio investigation on the core polarization effects without the need of employing parameterized model potential. We present in this paper quantitatively the change in atomic transition rate due to the core excitations for four-electron systems, especially for transitions involving doubly excited states and transitions with small oscillator strengths. Our numerical results using length and velocity gauge typically agree to better than 1%.

Theoretical Study of Atomic Rydberg States

Recently, a new microwave-optical method was developed by Wing and Lamb1for the experimental study of the atomic Rydberg states. The new technique, with a 104 -fold improvement in resolution over the conventional spectroscopic methods, makes it possible for the first time to obtain accurate details on the previously unresolved electrostatic fine structures. As emphasized by those authors, the physics of the atomic Rydberg states holds special theoretical interest not only because of its quasi-hydrogenic nature but also because of its close relation to the scattering of slow electrons by the charged ion core. Thus the experimental breakthrough has added great impetus to the search for a parallel progress in theory, the search for a general, first-principle approach, capable of improved quantitative predictions as well as qualitative interpretations. As an attempt along this direction, we have carried out a theoretical study on the electrostatic fine structure of the Rydberg series for atomic helium within the framework of the Brueckner-Goldstone2 many-body perturbation theory approach.