Kjell Aashamar

Oscillator Strengths in the Aluminum Sequence

The structures of the 3s23p 2P0 ground state and of a number of excited states for aluminum and ions along the isoelectronic sequence up to Ca VIII have been calculated in the Multiconfiguration Optimized Potential Model. The excited states include the following: 3s23d 2D, 3s24s 2S, 3s3p2 2D, 2S, as well as 3s24p, 3p3 and 3s3p(3P0)3d 2P0. There is strong configuration mixing in the spectroscopic terms but on the basis of our calculations we recommend a different designation from that currently adopted for the 3p3 and 3s3p(3P0)3d 2P0 terms. Oscillator strengths for transitions among these terms have been calculated in the length and velocity formulation with particular emphasis on accurate description in the vicinity of term crossings. Comparison is made with other theory and with experiment where results are available. At present, the experimental data are inadequate to verify the many calculated structures in the isoelectronic gf dependence.

Variational Perturbation Theory Study of Some Excited States of Two‐Electron Atoms

The Hylleraas–Scherr–Knight variational perturbation method has been applied to the two‐electron states 1s3s 3,1S and 1s3p 3,1P. The calculations have been carried through to 20th‐order wavefunctions, with 96‐, 126‐, and 162‐term expansions of the Hylleraas type, thus yielding estimates of the energy through the 41st order. The perturbation energy coefficients are tabulated through the 21st order for the states 1s2s 3,1S, 1s2p 3,1P, 1s3s 3,1S, and 1s3p 3,1P, and the corresponding nonrelativistic energies are presented for the first 10 elements of the helium isoelectronic sequence, with the exception of H− to which the perturbation expansions do not apply. Where comparison is possible, our results are in fair agreement with those obtained from conventional variational calculations. A survey of the variational perturbation procedure is also given, presenting the basic formulas and phrasing two important theorems.

Oscillator strengths and lifetimes for low-lying terms in the Al isoelectron sequence

We have calculated oscillator strengths in the length and velocity formulation for a large number of transitions in the Aluminum isoelectronic sequence from Si II through K VII, using the Multiconfiguration Optimized Potential Model. The results have been used to determine the lifetimes of 14 low-lying excited terms along the sequence. Comparison is made with experiment and with other theory where results are available. The agreement between our values and other theoretical results is generally good, although deviations do occur near level crossings. Some significant discrepancies between theory and experiment persist concerning lifetimes for S IV.

Energy Levels in the Magnesium Sequence, Mg I-Mn XIV, Calculated in the Multiconfiguration Optimized Potential Model

The energies of a large number of low-lying levels in the atoms and ions of the Magnesium isoelectronic sequence from Mg I to Mn XIV have been calculated in a configuration interaction calculation. The orbitals are determined as eigenfunctions of the one-particle Schrodinger equation for a central potential that is variationally optimized. A relativistic calculation using the Breit approximation is carried out in the potentials calculated non-relativistically. The results are generally in good agreement with experiment, but a number of possible reassignments are suggested. Singlet-triplet separations important for forbidden transition rates, and fine-structure intervals are also tabulated.

Oscillator strengths for transitions from 3s4s and 3s4p levels calculated in the magnesium sequence, MgI-MnXIV using the multiconfiguration optimized potential model

Oscillator strengths for downward transitions from the 3s4p and 3s4s levels in the Magnesium isoelectronic sequence are reported. These, as well as lifetimes for these levels, have been calculated for MgI to MnXIV using the Multiconfiguration Optimized Potential Model (MCOPM) with inclusion of relativistic corrections. Generally, the level splittings are reasonably accurate but at certain level crossings - occurring near Sv and C1VI - considerable energy level accuracy is required to ensure accurate relativistic mixing coefficients and transition rates. Corrections have been applied to the energies in these cases.

Variational perturbation theory investigations on two‐electron atomic systems. III. Nonrelativistic results for the state 1s 2s3S

The variational perturbation (HSK) procedure has been applied to the two‐electron atomic state 1s2s3S. The total nonrelativistic energies and corresponding wavefunctions have been determined with errors less than one part in 1012 and 1–2 parts in 106, respectively, for all Z ≥ 2. The results are presented in tables accompanied by illustrative figures.

Computer studies of the evolution of planetary and satellite systems I. Description of the program: Preliminary tests

In this paper we describe a CDC-Cyber 74 program for computer simulation of the evolution of a system consisting of a large number of objects in orbit around a central body or primary. Some preliminary tests done with the program will also be described.

Computer studies of the evolution of planetary and satellite systems

This paper describes two computer experiments carried out with a CDC-Cyber 74 program (Barricelliet al., 1979) for computer simulation of a large number of objects in orbit about a central body or primary. The first experiment was started with 125 planets of which the two largest ones had coplanar orbits and masses comparable to those of Jupiter and Saturn, respectively. Their semimajor axes and eccentricities were, however, much larger. The smaller planets had a distribution promoting the formation of an axial meeting area. The experiment gives information relevant to the question of focusing of planetary orbits into a common plane and to the question of the formation and stability of an axial meeting area. Together with the next experiment, it also gives information about the development of commensurabilities (or resonances) with the largest planets.The second experiment started with 55 planets none of them with a mass greater than about 20% of Jupiters but several of them with orbits close to a common plane. The aim of the experiment was to investigate whether successive captures followed by planetary fusion (Barricelli, 1972a) could lead to the formation of major planets comparable to Jupiter and Saturn, and in similar orbits. Also this experiment gives information relevant to the commensurability problem.

Oscillator strengths for transitions among low-lying quartet terms in the nitrogen isoelectronic sequence

We have calculated energies and transition rates for the 2s22p3 4S° ground state and a number of excited states in the isoelectronic sequence of atomic nitrogen using the multiconfiguration optimized potential model (MCOPM). The excited states include the 2s22p23s 4P, 2s2p4 4P, 2s22p23p 4D°, 2s22p23p 4P°, 2s22p23p 4S°, 2s22p23d 4F, 2s22p23d 4D and 2s22p23d 4P terms. The oscillator strengths for transitions among these terms have been calculated in both length and velocity gauge. Particular emphasis has been put on an accurate description near level crossings. Comparison with other theoretical and experimental results are made. However, the experimental data are rather sparse, and verification of many of the calculated trends against experiment is therefore not yet possible.

Relativistic transition rates for sextet levels in Cr II

Configuration interaction calculations have been carried out to obtain rates for electric dipole transitions and lifetimes for the 1s22s22p63s2 3p63d44d and 5s6D and 4d6F levels in Cr II. Up to 40 configurations have been included so correlation effects should be well accounted for. Relativistic interactions are included through the use of the Breit-Pauli hamiltonian to obtain the level wave functions and energies. Strong mixing of the 4d levels occurs and this leads to substantial departures from earlier nonrelativistic calculations that assume LS coupling for these states. Results include the actual compositions of both even and odd parity levels where significant mixing occurs and the rates for all transitions that are allowed to lower levels from these 4d and 5s levels.