Bengt Edlén

The Dispersion of Standard Air

By combining Barrell and Sears’ measurements in the visible and Koch’s and Traub’s in the ultraviolet, a dispersion formula for standard air has been derived, viz., (n−1)108=6432.8+2 949 810(146−σ2)−1+25 540(41−σ2)−1,σ being vacuum wave number in μ−1, which should satisfy all needs of precision spectroscopy, in particular for converting wavelengths in air into vacuum values.

Reference Wavelengths From Atomic Spectra in the Range 15 Å to 25000 Å

This is a compilation of atomic lines with accurately known wavelengths covering the range from 15 A to 25000 A. The tables are a fairly complete record of available spectrum lines that meet the requirements for useful references with regard to wavelength accuracy and intensity. In general, wavelength uncertainties range from 0.0001 A to 0.002 A. Section 1, λ > 2000 A, gives λair and λvac for 3341 lines belonging to thirteen different spectra of ten elements. Section 2, λ < 2000 A, contains 2091 lines belonging to 59 different spectra of 28 elements. The lines of section 2 are listed both by spectrum (i.e. element and ionization stage) and in a finding list arranged in order of decreasing wavelength. Detailed explanations of the data and the sources used for the compilation are included.

Comparison of Theoretical and Experimental Level Values of the n = 2 Complex in Ions Isoelectronic with Li, Be, O and F

The differences between observed and theoretical values of level intervals within the n = 2 complex in ions isoelectronic with Li, Be, O and F have been studied as functions of Z. The theoretical values are based on the tables of Cheng, Kim and Desclaux. For spin-orbit intervals, σ (theor) is taken as their multiconfiguration Dirac-Fock value with Breit correction (MCDF + B), for other intervals within the same configuration the Z-independent correlation energy from Cheng, Froese Fischer and Kim is added, and for interconfiguration intervals a Lamb-shift correction is also included, obtained by transforming the values of Cheng et al. into a smooth function of Z. The difference σ (obs) - σ (theor) is then expressed by the formula A + B(Z - C)-1 + a(Z - s)x, where the first two terms account for the residual correlation energy and the last term comprises all additional relativistic and radiative corrections. In a few cases we had to use two such terms with opposite sign and exponents differing by 2 to 3 units. The constants A, B, C, a and x are adjusted to fit the observations within their error limits. As compared to a fitted polynomial, the present formula is much better suited for extrapolation and provides a sharper test of the experimental data, especially at the high-Z end of a sequence. It has revealed a number of incorrect line identifications in the Be sequence. The results of the analyses are summarized in tables of recommended level values and wavelengths, extending to Z = 36 and in some cases to Z = 42. The wavelengths obtained for the resonance lines in the Be, O and F sequences may become useful as wavelength standards.

The Transitions 3s-3p and 3p-3d, and the Ionization Energy in the Na I Iso-electronic Sequence

Simple expressions in Z for the fine-structure intervals of 3p2P and 3d2D and for the transition energies 3s-3p and 3p-3d are derived from experimental data in the iso-electronic sequence of Na I-like spectra from S VI to Mo XXXII. The formulae provide a check on the accuracy of existing measurements and an easy interpolation of missing data. By a combination of the resulting energy values of 3d2D5/2,3/2 with the ionization energies of nf2F7/2,5/2, given by a formula based on the polarization concept, the series limits are derived from observations of the transitions 3d-nf. The results are summarized in a semi-empirical expression in Z for the ionization energy valid for Z ≥ 16. Finally, interpolation formulae are given for the line strengths of the transitions 3s-3p and 3p-3d based on calculations by A. W. Weiss.

Accurate Values of the Energy Intervals in the Configurations 1s22s22pk (k= 1-5)

Accurate values of the energy intervals in the ground configurations 2s22pk (k = 1-5) are derived from all available experimental data (including many forbidden lines observed in tokamaks) by comparing the observed values with the theoretical values calculated by Cheng, Kim and Desclaux and expressing the differences by low-degree polynomials in Z. The behaviour of the polynomials makes some extrapolation permissible, and level values and predicted wavelengths of forbidden lines are tabulated to Z = 36.

On the identification of Ar x and Ar xiv in the solar corona and the origin of the unidentified coronal lines

A study of theZ-dependence of the2P intervals of 2s22p and 2s22p5, aided by recent observational results, confirms the identification in the coronal spectrum of λ 4412 with Arxiv, and of λ 5533.4 with Arx. It is further shown that transitions from metastable levels in the configurations 3s23pk 3d, withk=3, 4 and 5, of Fexi,x, ix, and Nixiii, xiii, xi can well account for the remaining unidentified coronal lines.

Forbidden Lines in Hot Plasmas

A survey is given of the numerous forbidden lines that have recently been discovered in the spectra of tokamak plasmas. They represent magnetic-dipole transitions in three different groups of configurations: 2s2p and 2s22pk (k = 1–5), 3s3p and 3s23pk (k = 1–5), and 3dk (k = 1, 2, 8, 9). In the first group (n = 2) a total of 62 lines have been reported for Z = 21–32, in the second group 65 lines (some of which are given as tentative) for Z = 29–42, and in the 3dk group 8 lines for Z = 40, 42. The identifications in the n = 2 configurations have all been confirmed in elaborate isoelectronic studies of the transition energies. A corresponding investigation of the intervals in the second and third group of configurations is hampered by lack of suitable theoretical data, but provisional checks on the isoelectronic consistency of the identifications are presented.

A Critical Compilation of Energy Levels in the Configurations 2sm2pk(m=2, 1, 0) of F I-, O I- and Be I-like Spectra

Existing observations of transitions 2s22pk-2s2pk+1 and 2s2pk+1-2pk+2 in F I-, O I- and Be I-like spectra are collected and examined as to their isoelectronic consistency by plotting against Z appropriate functions of selected intervals. The functions are then expressed by polynomials of the fourth to the sixth degree, derived by a weighted least-squares fitting over a range of about twenty Z-values, up to Z = 33, 32 and 28 in the F I, O I and Be I sequences, respectively. In the case of the Be I sequence, a previous investigation is now extended with the aid of new observations by Lawson and Peacock for Z = 24-28. For all three sequences the results of the examination are presented in tables of recommended level values and recalculated wavelengths.

A Critical Survey of the Low Configurations in Be I-like Spectra

Available measurements of the transitions 2s2-2s2p and 2s2p-2p2 are examined as to their iso-electronic consistency by studying appropriate functions of the transition energies of 2s2 1S0-2s2p 1P1, 3P1, 2s2p 1P1-2p2 1D2, 1S0 and 2s2p 3P2-2p2 3P2, and by deriving semi-empirical screening formulae for the fine-structure intervals of the 3P terms. In this way, accidental experimental errors are smoothed out and missing data are determined by interpolation. The results of the analysis are comprised in a table of recommended level values, extending to Z = 26 or, for 2s2p 1P1, 3P1, to Z = 28. A comment on our recent discussion of the Li I-like spectra is appended.

The forbidden transitions within 3s2 3p5 3d of Fe ix and Ni xi and 3s2 3p4 3d of Fe x and Ni xii

Improved level values for 3s2 3p5 3d and 3s2 3p4 3d of Fe ix and Fe x are derived from the observed forbidden lines with special regard to recent accurate measurements in the vacuum-ultraviolet part of the coronal spectrum. A procedure for estimating expected relative intensities is proposed and used for an additional check on the consistency of the identifications, which now comprise 12 lines of Fe IX and 11 lines of Fe x. Finally, by use of a suitable extrapolation technique the wavelengths of corresponding lines in nickel are predicted, which leads to some new identifications and a total of 6 identified lines of Ni xi and 4 of Ni xii.