Kwong T. Chung

Energy and fine structure of 1s2np states (n=2,3,4 and 5) for the lithium isoelectronic sequence

The non-relativistic energies of 1s2np (n = 2, 3, 4 and 5) states for the lithium isoelectronic sequence from Li I to Ne VIII are calculated using the full-core plus correlation method. Relativistic and mass polarization effects on the energy are evaluated using first order perturbation theory. The fine structures are determined from the expectation values of the spin-orbit and spin-other-orbit interaction operators in the Pauli-Breit approximation. The higher order relativistic effects are estimated using the hydrogenic solution to the Dirac equation with an effective nuclear charge. The QED correction is also included. Our results are compared with the experimental and theoretical data in the literature. The fine structure results agree well with experiment. For 1s2np energies with n ≥ 3, it appears that our results are quite accurate for all Z investigated. However, for the 1s22p systems, the discrepancy with experiment grows monotonically from 0.5 cm−1 for Li I to 29 cm−1 for Ne VIII. This is very different from all the other 1s2nl systems we have investigated using the same method. What separates 1s22p apart from the others is the unusually large orbit-orbit interaction and mass polarization effects. For Z > 6, the expectation values of these perturbation operators are opposite in sign to those of the 1s2 core. This energy increases quickly with Z.

Dipole polarizabilities for the ground states of lithium-like systems from Z=3 to 50

The dipole polarizabilities of the lithium-like ground states, 1s22s 2S, are calculated with the full-core plus correlation (FCPC) wavefunctions. The non-relativistic polarizabilities are obtained by using a variation-perturbation method. Based on the relativistic and QED corrections to the energy, the dipole polarizabilities are corrected using an oscillator strength formula. The results indicate that relativistic and QED effects on the dipole polarizability become very important for Z>or=15. The result for Li I, 164.08 a03, is in good agreement with a recent CI-Hylleraas calculation, 164.1 a03 and with the experiment, 164.0+or-3.4 a03. The calculated results of other lithium-like systems are compared with previous theoretical results in the literature.

Electron affinity of lithium

The energy of the Li– 1s22s2 state is calculated with a configuration interaction (CI) wave function using a 1s2-core plus correlation method. Relativistic and mass polarization corrections are included. The energy upper bound obtained in this work is substantially lower than that of the Sims et al. [Phys. Rev. A13, 560 (1976)] where an elaborate Hylleraas wave function is used. From our energy upper bound and the core deficiency correction we found that the Li 1s22s electron affinity is greater than 0.6171 eV. Our extrapolated result, 0.6174(2)eV, agrees with the results, 0.6173(7)eV and 0.6176(2)eV from experiment.

Energy and fine structure of 1s2nd and 1s2n f states for the lithium isoelectronic sequence

The non-relativistic energies of 1s2nd (n=3,4 and 5) and 1s2nf (n=4 and 5) states for the lithium isoelectronic sequence from Li I to Ne VIII are calculated with a full-core plus correlation method using multiconfiguration interaction wavefunctions. Relativistic and mass-polarization effects on the energy are evaluated perturbatively as the first-order corrections. The fine structure is calculated by using spin-orbit and spin-other-orbit interaction operators. The authors results are in excellent agreement with experimental data in the literature. Possible misidentifications in the observed optical spectra are pointed out. They show that this full-core plus correlation method is useful for excited atomic systems with a 1s2 core.

Improved nonrelativistic energies for 1s22p systems using a restricted variation method

By using a restricted variation method, the nonrelativistic energies of the lithiumlike 1s22p systems are calculated. For lithium, the predicted nonrelativistic energy is –7.410 157 8(9)a.u. [Pipin and Bishop, Phys. Rev. A45, 2736 (1992)]. The results for systems with Z = 4-10 also give significant improvement over the recent results of Wang et al., Physica Scripta 47, 65 (1993). These results show that this restricted variation method could be very useful for high precision variation calculations.

On the Quartet System of B III

Theoretical and experimental investigations of the quartet system of B III have been undertaken. Numerous transitions not reported earlier are predicted with high accuracy. Experimentally a number of new transitions has been observed for the first time. Based on this work several lines from other experimental sources are reclassified. Oscillator strengths and lifetimes associated with these quartet states are also given. Finally an improved term diagram for the doubly-excited quartet levels in B III is presented on an absolute scale.

Resonances of helium in a DC field

A saddle-point complex-rotation method is used to study electric-field effects on the doubly excited resonances of He. By using a 892-term wavefunction, a seven-angular-symmetry calculation (i.e. Lmax = 6) is performed for a comprehensive study around the He (2, 6a) 1Po and (2, 6a) 1De resonance pair in the presence of an external electric field. A general M-state sum rule is shown which suggests the sum of total energy or total width of M-state system is not affected by the presence of a weak static field. The M-state sum rule is used to investigate the sharing of resonance energies and widths for the locally isolated resonance groups around the He (2, 6a) 1Po and (2, 6a) 1De resonance pair in the small-field region.

Doubly excited states in B III

In a beam-foil study of boron at wavelengths between 400 A and 1200 A, we have been able to identify many transitions within the doubly-excited quartet system of B III. These identifications are confirmed in some cases by transitions in the near ultraviolet observed from the same terms. We shall compare our experimental term energies with recent calculations for this isoelectronic sequence and discuss recent observations in other series members. We list many newly observed transitions of B IV.

Energy and lifetime of triply excited states of lithium-like beryllium and carbon

Seven triply excited states of lithium-like beryllium and carbon are calculated with the multichannel saddle-point and saddle-point complex-rotation methods. Relativistic effects are included using first-order perturbation theory. The widths are studied with one open channel at a time as well as fully coupled open channels. The predicted Auger branching ratio is compared with the observed spectra. The radiative transition rates are also calculated. These results are compared with the theoretical data in the literature.

Identification of doubly- and triply-excited Be+ resonances in a high-resolution Auger spectrum

The energies and wavefunctions of thirteen doubly-excited and nine triply-excited resonances of Be+ are calculated using the saddle point technique. These results are used to make identifications in the Be+ Auger spectra observed by Rodbro et al. (1979). For all within the experimental uncertainty quoted. For the triply-excited resonances, fourteen Auger lines are identified. These identifications are compared with those found for triply-excited lithium. The strong similarities found between these systems provides supporting evidence that both identifications are probably correct.