J.E. Hansen

Forbidden Transitions in 3p4 and 4p4 Configurations

We have calculated energy levels and radiative transition probabilities in the ground configurations of the sulfur and selenium isoelectronic sequences up to molybdenum and silver, respectively. Transition probabilities have been obtained for M1 and E2 forbidden lines within the p4 configurations using electrostatic and spin-orbit integrals for the interactions within this configuration deduced by a fitting procedure to the available experimental energy levels or by graphical inter(extra)polation of Slater parameters along the sequence when the energy levels are unknown. Some of the most important configuration interaction and relativistic effects have been included explicitly using the HFR self-consistent method due to Cowan and Griffin. For most of the ions in the selenium sequence, transition probabilities are reported for the first time. The effects of including configurations with 4f electrons explicitly have been studied for both the 3p3 and 3p4 configurations.

Magnetic-dipole and electric-quadrupole transitions in the ground-state configurations of the germanium and arsenic isoelectronic sequences

Calculations of energies and transition probabilities are reported for forbidden lines in the ground configurations of the germanium (4p2) and arsenic (4p3) isoelectronic sequences up to silver (Z = 47). Configuration interaction and relativistic effects were included in the framework of the HXR and HFR self-consistent-field methods. Transition probabilities have been obtained in intermediate coupling using parameter values for the 4p2 and 4p3 configurations obtained either by fitting or by extra-(inter)polation when experimental energy levels are missing. Except for Ge I and As I, transition probabilities are reported for the first time for all these ions. A note concerning transition probabilities for Fe XII is also appended.

Fine-structure analyses with orthogonal operators

The single-electron operator representing the spin-orbit interaction in the 3d shell is augmented by a collection of operators, each of which acts on two electrons at a time and possesses identical ranks k in the spin and orbital spaces with k=1 or 2. Orthogonality is guaranteed by labelling each operator by a distinct set of irreducible representations of various Lie groups. The operators are able to represent all terms deriving from the non-relativistic limit of the Breit interaction for 3d electrons as well as those terms deriving from the leading types of electrostatically correlated spin-orbit (EL-SO) effects. Fits to the experimental data of Cr IV 3d3 and Ni IV 3d7 yield mean errors of only 1.91 and 3.87 cm-1 respectively. A comparison of the values of fine-structure parameters with those deduced from Hartree-Fock calculations gives good agreement for Cr IV 3d3 apart from a single parameter that is particularly sensitive to EL-SO.

The importance of continuum d states for the interaction nsnp6↔ns4d in the rare gases

Calculations are described of the interaction between the nsnp6 2S term and the ns2np4md/ epsilon d2S series in atoms isoelectronic with the halogens, particularly the rare gases. For the halogens, it has been found earlier that the interaction with the continuum d series is crucial for a correct description of the term structure. A similar, although weaker, effect of the continuum is established for the rare gases. Detailed results for the admixture of nsnp6 2S in bound and continuum d states are reported for Cl I, Ar II, K III and Kr II. Only in K III is the effect of the continuum found to be negligible. The present results are important for the interpretation of satellite structures connected with the ejection of an ns electron from the rare gases. It is shown that there is good agreement between the present calculations and the satellite intensities in photoelectron experiments. The experimental uncertainties in photoelectron experiments are at present the limiting factors in the comparison and the need for better experimental values in order to test the calculations is stressed. Disagreements are found between the calculations and the results of (e, 2e) experiments. These disagreements are attributed to difficulties in the interpretation of the (e, 2e) experiments.

The influence of core excitations on energies and oscillator strengths of iron group elements

We show that for configurations of the type 3pM3dN the influence of core excitations, in particular the excitation 3p2 to 3d2, is important both for energies and oscillator strengths. The latter is particularly true for transitions of the type 3p63dN to 3p53dN+1 due to the fact that the core excitation in the ground configuration leads to a configuration which has an allowed dipole transition to the excited state. Differences and similarities between 3p53dN and the more extensively studied 3p63dN configurations are pointed out and illustrated with several examples concerning highly charged ions. The conclusion is that, while core excitations are important for the description of transitions out of the open 3d shell, they are absolutely essential for transitions out of the closed 3p shell, gf values are given for astrophysically important transitions in Ni X.

MCHF oscillator strength and lifetime calculations in neutral calcium

The authors report extensive multiconfiguration Hartree-Fock (MCHF) calculations, taking into account valence correlation and core-relaxation effects, of energy levels, eigenvector compositions, electric dipole and quadrupole oscillator strengths involving the n1S(n=1-4), n1PO (n=1, 2), n1D(n=1-3) and n1FO(n=1, 2) states in Ca I. On the whole, the agreement between theory and observation has been improved by their set of MCHF results. The theoretical transition probabilities allow the evaluation of the lifetimes for the levels 4s4p, 4s5p 1PO; 4s4d, 4p2 1D and 3d4p, 4s4f 1FO which are compared with previous measurements. The differences between MCHF calculations for series perturbed by doubly-excited states in Ca and Sr are discussed. It is concluded that core-polarization effects are of about the same importance in the two atoms but that the effects on the 3d (Ca) and 4d (Sr) orbitals are such that the total core-polarization effects for series and perturbers are of the same magnitude in Sr while large differences exist in Ca.

Parametric fitting with orthogonal operators

The use of orthogonal operators for parametric fitting of energy level positions in complex configurations is reviewed and the properties of such operator sets are discussed using simple examples.

Transition Probabilities for Forbidden Lines in the Ground-State Configuration of the Bromine Isoelectronic Sequence

Calculations of transition probabilities are reported for the magnetic dipole and electric quadrupole components of the ground-state transition in the 4p5 configuration of the bromine sequence up to Xe XX. The relativistic Hartree-Fock (HFR) self-consistent-field method was used combined with parametric fitting in a configuration interaction approach. The results reported here are an extension of similar calculations recently reported in 3pN and 4pN configurations, and some comments on the effect of 3p → 4f excitations in 3p1 and 3p5 configurations are given together with a discussion of the relative merits of the HFR and HXR methods for the calculation of spin-orbit integrals.

Radiative transition rates in the ground configuration of the phosphorus sequence from argon to ruthenium

New calculations of transition probabilities are presented for forbidden lines in the ground configuration of the phosphorus sequence from Ar to Ru. Relativistic contributions and configuration interaction effects were included in the framework of the HXR and HFR self-consistent-field methods. Energy levels and A values were computed in intermediate coupling with fitted or interpolated semi-empirical energy parameters. The variation in magnetic dipole and electric quadrupole oscillator strengths as a function of Z is extended beyond nickel to Z = 44.

A revised analysis of the spectrum of Ar III

A revised and extended analysis of the optical spectrum of Ar III is presented. All the energy levels in the 3s23p4, 3s3p5, 3s03p6, 3s23p34s, 4p and 3d configurations are reported. Nearly all the singlet terms, which are of particular interest in Auger spectroscopy are new. An interpretation of the odd configurations based on a newly introduced orthogonal parameter set for pNd configurations is reported. The strong mixing between parent terms in the 3p33d configuration is noted and some consequences for the spectroscopy of Arn++Ar collisions are discussed. A comparison with Auger results for the LMM transitions in Ar is given.