The spectrum and term system of S VIII

Abstract

The spectrum of seven times ionized sulfur, S VIII, has been observed in the wavelength range 50-1200 A. Both beam-foil and laser-produced plasma light sources have been used. 71 new Lines representing the transitions 2p5-2p43d, 2p43s-3p, 3 p 3 d , 3d-4J 4f-5g and 5g-6h have been identified and 100 energy levels, of which 46 are new, are now accurately established. The spectral analysis is supported by isoelectronic comparisons along the F I-sequence and by parametric least-squares fits of Slater integrals to the observed levels. The ionization potential in S VI11 is determined to 2651 899 * 6Ocm-' and estimated ionization energjes are derived for the isoelectronic elements between F I and Ar X.

Wavelengths, Energy Levels, Lifetimes, and Weighted Oscillator Strengths for the S Viii Spectrum

“…Martin et al (1990) adopted 10085 cm −1 , an average of the values found by Edlén and by Curtis & Ramanujam. A very accurate comparison between experimental data and theoretical multi-configurational Dirac-Fock calculations was performed by Kim & Huang (1982), producing an interval of 10081 ± 5 cm −1 . Bengtsson et al (1993), using almost the same data set as we used in the present work, found 10087 ± 19 cm −1 . Isoelectronic studies of the fluorine sequence include data about F i (Lidén 1950), Ne ii (Persson 1971), Na iii Nietsche 1972 and, Mg iv (Johannesson et al 1972, Artru & Kaufman 1972, and Johannesson & Lundström 1973, Al v Brillet 1974 andArtru 1975), Si vi (Artru & Brillet 1977, Trigueiros et al 1991, and Trigueiros et al 1992, P vii (Fawcett et al 1970 andFawcett 1986), Cl ix (Bashkin et al 1973 andJupén 1985), Ar x (Bengtsson et al 1994, Fawcett et al 1978, and Lepson et al 2003, K xi (Jupén & Träbert 2001), Sc xiii and V x , and Ti xiv .…”

“…Almost all lines with wavelengths below 50 Å are from Ferner (1948), except one line from Fawcett et al (1974), and another from Fawcett & Hayes (1987). Above 50 Å, most lines are from Bengtsson et al (1993) and from Cohen, as quoted by them. The complete list of lines, their uncertainties, and sources is in Table 1.…”

“…A compilation of lines from S i to S xvi lines was published by Martin et al (1990) covering all experimental energy levels known at the time. In an extensive work, Bengtsson et al (1993) studied S viii in the interval from 50 to 1200 Å. Their analysis of 2p 5 -3d, 3s-3p, 3p-3d, 3d-4f, 4f-5g, and 5g-6h transitions allowed the identification of 71 lines and 46 energy levels for the first time.…”

“…Lepson et al (2005) measured the sulfur emission spectrum from 20 to 75 Å using the electronbeam ion trap technique, but most of their results disagree in wavelength with all previous work. Dere et al (2009), using the data from Fawcett & Hayes (1987) and from Bengtsson et al (1993), were able to find new levels in 4s and 4d configurations. Their work, published in the CHIANTI database (Dere et al 1997), contains many line reclassifications for S viii spectra, mainly based on the theoretical work of Witthoeft et al (2007).…”

CHIANTI – an atomic database for emission lines

“…The experimental energy levels for the n = 2 levels are taken from Edlén (1983), while those for the n = 3 levels come from Fawcett & Hayes (1987) and Bengtsson et al (1993). The effective collision strengths were published by Witthoeft et al (2007b) for the 4.1 ≤ log T ≤ 8.1 temperature range but we used them only in the 4.5 ≤ log T ≤ 7.3 range to improve the fit of the original data in the range where S viii has significant fractional abundance.…”