Physics:Spectroscopy of multiply ionized atoms

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This branch of spectroscopy deals with radiation related to atoms that are stripped of several electrons (multiply ionized atoms (MIA), multiply charged ions, highly charged ions). These are observed in very hot plasmas (laboratory or astrophysical) or in accelerator experiments (beam-foil, electron beam ion trap (EBIT)). The lowest exited electron shells of such ions decay into stable ground states producing photons in VUV, EUV and soft X-ray spectral regions (so-called resonance transitions).

History

After Newton's.[1] discovery of spectral structure of white light (17th century) and subsequent studies of the nature of light (Hooke,[2] Huygens,[3] Young[4][5]) J. Fraunhofer[6] observed and measured dark lines in the Sun's spectrum (they bear now his name although several of them were observed earlier by Wollaston[7]). It may be the first example of fundamental research in spectroscopy.

Later Bunsen and Kirchhoff[8] found that Fraunhofer lines correspond to emission spectral lines observed in laboratory light sources, and so they laid way for spectrochemical analysis in laboratory and astrophysics.

In the 19th century new developments such as the discovery of photography, Rowland's[9] invention of the concave diffraction grating, and Schumann's[10] works on discovery of vacuum ultraviolet (fluorite for prisms and lenses, low-gelatin photographic plates and absorption of UV in air below 185 nm) made advance to shorter wavelengths very fast. At the same time Dewar[11] observed series in alkali spectra, Hartley[12] found constant wave-number differences, Balmer[13] discovered a relation connecting wavelengths in the visible hydrogen spectrum, and finally Rydberg[14] derived a formula for wave-numbers of spectral series.

The first decade of the 20th century brought the basics of quantum theory (Plank,[15] Einstein[16]) and interpretation of spectral series of hydrogen by Lyman[17] in VUV and by Paschen[18] in infrared. Ritz[19] formulated the combination principle.

In 1913 Bohr[20] formulated his quantum mechanical model of atom. This stimulated empirical term analysis (see references in,[21] page 83).

Between 1920 and 1930 fundamental concepts of quantum mechanics were developed by Pauli,[22] Heisenberg,[23] Schrödinger,[24] and Dirac.[25] Understanding of the spin and exclusion principle allowed conceiving how electron shells of atoms are filled with the increasing atomic number.

Structure studies

Further progress in studies of atomic structure was in tight connection with the advance to shorter wavelength in EUV region. Millikan,[26] Sawyer,[27] Bowen[28] used electric discharges in vacuum to observe some emission spectral lines down to 13 nm they prescribed to stripped atoms. In 1927 Osgood[29] and Hoag[30] reported on grazing incidence concave grating spectrographs and photographed lines down to 4.4 nm (Kα of carbon). Dauvillier[31] used a fatty acid crystal of large crystal grating space to extend soft x-ray spectra up to 12.1 nm, and the gap was closed. In the same period Manne Siegbahn constructed a very sophisticated grazing incidence spectrograph that enabled Ericson and Edlén[32] to obtain spectra of vacuum spark with high quality and to reliably identify lines of multiply ionized atoms up to O VI, with five stripped electrons. Grotrian[33] developed his graphic presentation of energy structure of the atoms. Russel and Saunders[34] proposed their coupling scheme for the spin-orbit interaction and their generally recognized notation for spectral terms.

Accuracy

Theoretical quantum-mechanical calculations become rather accurate to describe the energy structure of some simple electronic configurations. The results of theoretical developments were summarized by Condon and Shortley[35] in 1935.

Edlén thoroughly analyzed spectra of MIA for many chemical elements and derived regularities in energy structures of MIA for many isoelectronic sequences (ions with the same number of electrons, but different nuclear charges). Spectra of rather high ionization stages (e.g. Cu XIX) were observed.

The most exciting event was in 1942, when Edlén[36] proved the identification of some solar coronal lines on the basis of his precise analyses of spectra of MIA. This implied that the solar corona has a temperature of a million degrees, and strongly advanced understanding of solar and stellar physics.

After the WW II experiments on balloons and rockets were started to observe the VUV radiation of the Sun. (See X-ray astronomy). More intense research continued since 1960 including spectrometers on satellites.

In the same period the laboratory spectroscopy of MIA becomes relevant as a diagnostic tool for hot plasmas of thermonuclear devices (see Nuclear fusion) which begun with building Stellarator in 1951 by Spitzer, and continued with tokamaks, z-pinches and the laser produced plasmas.[37][38] Progress in ion accelerators stimulated beam-foil spectroscopy as a means to measure lifetimes of exited states of MIA.[39] Many various data on highly exited energy levels, autoionization and inner-core ionization states were obtained. 

New data

Simultaneously theoretical and computational approaches provided data necessary for identification of new spectra and interpretation of observed line intensities.[40] New laboratory and theoretical data become very useful for spectral observation in space.[41] It was a real upheaval of works on MIA in USA, England, France, Italy, Israel, Sweden, Russia and other countries[42][43]

A new page in the spectroscopy of MIA may be dated as 1986 with development of EBIT (Levine and Marrs, LLNL) due to a favorable composition of modern high technologies such as cryogenics, ultra-high vacuum, superconducting magnets, powerful electron beams and semiconductor detectors. Very quickly EBIT sources were created in many countries (see NIST summary[44] for many details as well as reviews[45][46]).

A wide field of spectroscopic research with EBIT is enabled including achievement of highest grades of ionization (U92+), wavelength measurement, hyperfine structure of energy levels, quantum electrodynamic studies, ionization cross-sections (CS) measurements, electron-impact excitation CS, X-ray polarization, relative line intensities, dielectronic recombination CS, magnetic octupole decay, lifetimes of forbidden transitions, charge-exchange recombination, etc.

References

  1. Newton, I. (1730). Opticks. Dover, New York, 1952, 4th ed.: London. https://books.google.com/books?id=GnAFAAAAQAAJ&pg=PP1. 
  2. Hooke, Robert (1665). Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon…. pp. 47. http://digicoll.library.wisc.edu/cgi-bin/HistSciTech/HistSciTech-idx?id=HistSciTech.HookeMicro. 
  3. Huygens, Christiaan (1690). Traité de la lumière. Leyden (published 1962). http://www.gutenberg.org/ebooks/14725. 
  4. "II. The Bakerian Lecture. On the theory of light and colours". Philosophical Transactions of the Royal Society of London (The Royal Society) 92: 12–48. 1802. doi:10.1098/rstl.1802.0004. ISSN 0261-0523. 
  5. Thomas Young (1855). "On the Theory of Light and Colours". in George Peacock. Miscellaneous works of the late Thomas Young Volume 1. London. p. 140. https://archive.org/details/miscellaneouswo01youngoog/page/n183. 
  6. Fraunhofer, J. (1817). "Bestimmung des Brechungs- und des Farbenzerstreuungs-Vermögens verschiedener Glasarten, in Bezug auf die Vervollkommnung achromatischer Fernröhre". Annalen der Physik 56 (7): 264–313. doi:10.1002/andp.18170560706. Bibcode1817AnP....56..264F. https://zenodo.org/record/1423482. 
  7. Wollaston, W. H. (1802). "A method of examining refractive and dispersive powers, by prismatic reflection". Philos. Trans. R. Soc. 92: 365–380. doi:10.1098/rstl.1802.0014. 
  8. Bunsen, R.; Kirchhoff, G. (1861). "Untersuchungen über das Sonnenspektrum und die Spektren der Chemischen Elemente". Abhandl. KGL. Akad. Wiss. Berlin. 
  9. Rowland, H.A. (1882). "LXI. Preliminary notice of the results accomplished in the manufacture and theory of gratings for optical purposes". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 13 (84): 469–474. doi:10.1080/14786448208627217. https://zenodo.org/record/2165693. 
  10. Schumann's papers are listed in T. Lyman, The Spectroscopy of the Extreme Ultraviolet (Longmans, Green and Company, London, 1928), 2nd ed.
  11. Liveing, G.D.; Dewar, J. (1879). "V. On the spectra of sodium and potassium". Proc. Roy. Soc. Lond. 29 (196–199): 398–402. doi:10.1098/rspl.1879.0067. 
  12. Hartley, W.N. (1883). "On Homologous Spectra". J. Chem. Soc. Lond. 43: 390–400. doi:10.1039/CT8834300390. 
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  14. Rydberg, J.R. (1890). "Recherches sur la constitution des spectres d'émission des éléments chimiques". KGL. Svenska Vetensk.-Akad. Handl., Stockh. 23 (11). 
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  16. Einstein, Albert (1905). "On a Heuristic Viewpoint Concerning the Production and Transformation of Light". Annalen der Physik 17: 132–148. http://lorentz.phl.jhu.edu/AnnusMirabilis/AeReserveArticles/eins_lq.pdf. 
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  21. Edlén, B. (1964). "Atomic Spectra". Handbuch der Physik 27: 80–220. 
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  23. Heisenberg, W. (1925). "Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen". Zeitschrift für Physik 33 (1): 879–893. doi:10.1007/BF01328377. Bibcode1925ZPhy...33..879H. 
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  30. Hoag, J.B. (1927). "Wavelengths of Carbon, Oxygen, and Nitrogen in the Extreme Ultraviolet with a Concave Grating at Grazing Incidence". Astrophys. J. 66: 225–232. doi:10.1086/143083. Bibcode1927ApJ....66..225H. 
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