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News on fundamental reference data
Specmchimica
Acta,
Vol. 49B. No. 8, pp. 811-814. 1994 Elsevier Science Ltd in Great Britain. All rights reserved 0x54-8547/94 $7.00 + 00
Copyright @ 1994
Printed
058&8547(94)ooo41-7
News on fundamental
reference data
PAUL B. FARNSWORTH Department of Chemistry, BrighamYoung University, Provo, UT 846024672, U.S.A. INTERNET:[email protected] (Received 9 May 1994)
THIS COLUMNwill
be a departure from the norm in that, rather than focusing my attention on the most recent work in the area of fundamental atomic reference data, I would like to devote most of the column to the long-term efforts of a single group, the Laser Spectroscopy Group at the CSIRO Division of Materials Science and Technology. The decision to do so is prompted by a feeling that my predecessor and I have been guilty of a degree of scientific provincialism. We have frequent contact with scientists in the United States and Western Europe, but much rarer interaction with scientists in other parts of the world. In past editions of this column we have ignored the important work by the Laser Spectroscopy Group at CSIRO that has spanned nearly two decades. This edition of the column is an attempt to correct that oversight and to bring to the attention of analytical spectroscopists a number of important contributions to the pool of fundamental data on atoms. The CSIRO Laser Spectroscopy Group was established in 1978 and built on the pioneering atomic absorption work of Sir ALAN WALSH and his colleagues. The Project Leader and Chief Research Scientist is Dr PETER HANNAFORD. Other permanent members of the group are: Senior Research Scientist DAVID GOUGH, Principal Research Scientists PETER LARKINS, MARTIN LOWE and RUSSELLMCLEAN, and Honorary Fellow Sir ALAN WALSH. The group is active in several areas related to the production of fundamental atomic data. These include: The use of cathodic sputtering as a universal means of producing atoms and singly charged atomic ions for subsequent study by time-resolved fluorescence and high-resolution Doppler-free laser spectroscopies. The time-resolved fluorescence spectroscopy is used in the determination of atomic lifetimes, absolute oscillator strengths, and Land6 g factors. The Doppler-free laser spectroscopy is used in the determination of hyperfine structures and isotope shifts of atomic resonance lines. The application of Doppler-free laser spectroscopy as a technique for the determination of isotopic abundances of elements. The development of diode lasers as high-resolution sources for atomic spectroscopy. Laser cooling and trapping of neutral atoms and the application of this technique to the development of an atom matter-wave interferometer. Over the past decade, the group has produced a series of reviews on work in the first area described above. Listed in chronological order, they are: Spectroscopy with sputtered atoms, Confemp. Phys. 24,251 (1983). and R. M. Lowe, Determination of atomic lifetimes using laserinduced fluorescence from sputtered metal vapor, Opt. Eng. 22, 532 (1983). 3. P. Hannaford, Laser spectroscopy beyond the sodium D lines, The Australian Physicist 23, 4 (1986). 4. P. Hannaford and R. M. Lowe, Some recent developments in atomic lifetime determinations, Aus?. J. Phys. 39, 829 (1986). 1. P. Hannford,
2. P. Hannaford
811
812
P. B. FARNSWORTH
5.
P. Hannaford and A. Walsh, Sputtered atoms in absorption and fluorescence spectroscopy, Spectrochim. Acta 43B, 1053 (1988). 6. P. Hannaford, Laser spectroscopy with sputtered atoms, Proceedings of the Ninth National Conference on Atomic and Molecular Physics, Bombay (1992), in press.
During the same time period the group has generated an impressive list of research papers. The papers dealing with fundamental atomic data are easily separated into two groups. The first group includes measurements of lifetimes, oscillator strengths and transition probabilities: 1. D. S. Gough, P. Hannaford and R. M. Lowe, Radiative lifetimes and oscillator strengths in neutral iridium, J. Phys. B: At. Mol. Phys 16, 785 (1983). 2. P. Hannaford and R. M. Lowe, Radiative lifetimes in MO II, J. Phys. B: At. Mol. Phys. 16, 4539 (1983). 3. P. Hannaford and R. M. Lowe, Radiative lifetimes in Fe II using selective laser excitation, J. Phys. B: At. Mol. Phys. 16, L43 (1983). 4. E. Biemont, N. Grevesse, P. Hannaford, R. M. Lowe and W. Whaling, A redetermination of the solar abundance of molybdenum, Astrophys. J. 275, 889 (1983). 5. W. Whaling, P. Hannaford, R. M. Lowe, E. BiCmont and N. Grevesse, Lifetimes, branching ratios and transition probabilities in MO I, J. Quunt. Spectrosc. Radiat. Transfer 32, 69 (1984). 6. P. Hannaford, R. M. Lowe, E. BiCmont and N. Grevesse,
Radiative lifetimes for Nb II and the problem of solar abundance of niobium, Asfron. Asfrophys. 143, 447 (1985). 7. P. Hannaford and R. M. Lowe, Radiative lifetimes of low-lying levels in Sm I, J. Phys. B: At. Mol. Phys. 18, 2365 (1985). 8. W. Whaling, P. Hannaford, R. M. Lowe, E. BiCmont and N. Grevesse, Absolute transition probabilities in vanadium I and solar abundance of vanadium, Asfron. Astrophys. 153, 109 (1985). 9. E. Biemont, N. Grevesse, P. Hannaford and R. M. Lowe, Lifetimes in Sm II and the solar abundance of samarium, Astron. Astrophys. 222, 307 (1989). 10. R. M. Lowe and P. Hannaford, Radiative lifetimes in Ti I, 2. Phys. D 21, 205 (1991). 11. P. Hannaford, R. M. Lowe, N. Grevesse and A. Noels, Lifetimes in Fe II and the solar abundance of Iron, As&on. Astrophys. 2J9, 301 (1992). 12. E. Biemont and R. M. Lowe, Radiative lifetime measurements in Dy II and the solar abundance of dysprosium, Astron. Astrophys. 273, 665 (1993). 13. R. M. Lowe, P. Hannaford and A.-M. Mktensson-Pendrill, Radiative lifetimes of the 6p2Pln and 6pzP,, levels in Yb II, 2. Phys. D 29, 39 (1994). The second group of papers includes the measurements isotope shifts by Doppler-free laser spectroscopy:
of hyperfhte splittings and
1. D. S. Gough and P. Hannaford, Very high resolution laser saturation spectroscopy in hollow-cathode and glow discharges, Optics Comm. 55, 91 (1985). 2. D. S. Gough, P. Hannaford, R. M. Lowe and A. P. Willis, Hyperfine structures in 51V using laser saturation spectroscopy in a hollow-cathode discharge, J. Phys. B: At. Mol. Phys. 18, 3895 (1985). 3. R. J. McLean, P. Hannaford, H.-A. Bachor, P. T. H. Fisk and R. J. Sandeman, Absorption line narrowing measurements of hyperfme structure in highly excited levels of yttrium, 2. Phys. D 1, 253 (1986). 4. D. S. Gough and P. Hannaford, High quality saturated absorption spectroscopy in a sputtered vapour: application to hyperfine structure in Zr I, Optics Comm. 67, 209 (1988). 5. P. Hannaford and D. S. Gough, High quality saturated absorption spectroscopy in a sputtered vapour: application to isotope shifts in Zr I, Laser Spectroscopy IX, Proceedings
of the Ninth International Conference
on Laser Spectroscopy,
News on fundamentalreference data
6.
7. 8. 9.
10. 11.
813
Eds M. S. Feld, J. E. Thomas and A. Mooradian, pp. 83-85. Academic Press, Boston (1989). A. W&utstriim, D. S. Gough and P. Hannaford, Hyperfine structure measurements in tantalum I using laser saturation spectroscopy in a sputtered vapour, 2. Phys. 22, 723 (1992). P. Hannaford, Hyperfine structure and isotope shifts in the 595.5nm (a3&-z5F1) ground-state transition in Zr I, Opt. Lett. 17, 432 (1992). P. L. Larkins and P. Hannaford, Precision energies and hyperfine structures of the 5~5p~P”~,i,~ and 5s 6r3S1 levels in II, 2. Phys. 27, 313 (1993). R. J. McLean, P. Hannaford, P. L. Larkins and W. J. Rowlands, Diode laser saturated absorption measurements of isotope shifts and hyperfine structure of Zr I, Optics Comm. 102, 43 (1993). A. Wgnnstriim, D. S. Gough and P. Hannaford, High resolution laser spectroscopy in yttrium ions in a sputtered vapour, Z. Phys. D 29, 39 (1994). A.-M. M&ensson-Pendrill, D. S. Gough and P. Hannaford, Isotope shifts and hypetfme structure in the 369.4 nm 6*&&j *PID resonance line of singly ionised ytterbium, Phys. Rev. A 49 (in press).
The consistently high level of productivity of the CSIRO laser group in the area of atomic reference data calls for continued attention to the group’s work by the analytical spectroscopic community. Other reference data news
In the previous two editions of this column [l, 21, I have made reference to the opacity project and its database, TOPbase. A limitation of that database that was not mentioned is that the f-values included in the database are for multiplets only, not for individual spectral lines. Data for individual lines can be readily calculated in cases of rigorous LS coupling. For many atoms, however, including C, N, and 0, such an approach can lead to large errors. WOLFGANGWIE~E at NIST has supplied me with references for calculated transition probabilities for those three elements that are done in intermediate coupling, and which provide data for individual lines of neutral carbon [3], nitrogen [4] and oxygen [5]. Since the last edition of the column, the Atomic Energy Level Data Center at NIST has published three volumes that will be of interest to the analytical spectroscopist. The first is a continuation of the series Selected Tables of Atomic Spectra begun by CHARLOTTE MOORE[6]. It is a compilation of energy levels and wavelengths for singly ionized oxygen (0 II). The second is a compilation of energy levels for all ionization stages of germanium (Ge I-Ge XXXII) [7]. In the final volume, JEAN GALLAGHERhas added to the legacy of CHARLOYTEMOORE by compiling under one cover Moore’s energy level and multiplet tables for hydrogen, carbon, nitrogen and oxygen atoms and ions [8]. With the exception of the 0 II data, the material in the tables has been published previously as sections of the series, Selected Tables of Atomic Spectra. The 0 II data were extracted from Ref. [6] above. Interest in solar abundances of iron-group elements continues to be a driving force for the generation of lifetime and wavelength data for those elements. Radiative lifetimes determined by laser-induced fluorescence and branching ratios determined by Fourier transform emission spectroscopy have been combined to determine the transition probabilities for 100 Ti II emission lines [9]. Transition probabilities for 550 Fe II lines have been determined from photographic solar spectra recorded on the Naval Research Laboratory normal incidence spectrometer aboard Skylab [lo]. Spectra from Fe hollow cathode lamps recorded on a combination of Fourier transform and grating instruments have been used to identify 86 new highly excited Fe I energy levels and to revise the energies of 110 previously reported levels [ll]. In a companion paper, 2200 lines from highly excited Fe I levels were identified, 1700 of which have been observed in the solar spectrum [12]. As a final note, a new set of calculations of energy levels and oscillator strengths for neutral calcium has recently been published [13]. The calculations are based on
814
P. B. FARNSWORTH
the configuration interaction method, and differ from previous calculations in that the Hamiltonian for the two valence electrons was modified by the addition of a semiempirical polarization potential. The results of the calculations are in better agreement with experiment than are previously reported theoretical values. REFERENCES [l] [2] [3] [4] [5] [6] [7] [8] [9] [lo] [ll] [12] [13]
P. B. Farnsworth, Specrroc~im. Acta 48B, 1301 (1993). P. B. Farnsworth, Spectrochim. Acta 48B, 1651 (1993). A. Hibbert, E. Bibmont, M. Godefroid and N. Vaeck, A&on. Astrophys. Suppl. Ser. 99, 179 (1993). A. Hibbert, E. BiCmont, M. Godefroid and N. Vaeck, Astron. Astrophys. Suppl. Ser. 88, 505 (1991). E. Bitmont, A. Hibbert, M. Godefroid, N. Vaeck and B. C. Fawcett, Astrophys. 1. 375, 818 (1991). W. C. Martin, V. Kaufman and A. Musgrove, J. Phys. Chem. Ref. Data 22, 1179 (1993). J. Sugar and A. Musgrove, J. Phys. Chem. Ref. Data 22, 1213 (1993). C. E. Moore, Tables of Spectra of Hydrogen, Carbon, Nitrogen, and Oxygen Atoms and Ions, Ed. J. W. Gallagher. CRC Press, Boca Raton, FL (1993). A. Bizzarri, M. C. E. Huber, A. Noels, N. Grevesse, S. D. Bergeson, P. Tsekeris and J. Lawler, Astron. Astrophys. 273, 707 (1993). J. 0. Ekberg and U. Feldman, Astrophys. J. Suppl. Ser. 86, 611 (1993). G. Nave and S. Johansson, Astron. Astrophys. 274, %l (1993). G. Nave and S. Johansson, Astron. Astrophys. Suppl. Ser. 102, 269 (1993). J. Miltroy, 1. Phys. B: At. Mol. Phys. 26, 3703 (1993).
Acta,
Vol. 49B. No. 8, pp. 811-814. 1994 Elsevier Science Ltd in Great Britain. All rights reserved 0x54-8547/94 $7.00 + 00
Copyright @ 1994
Printed
058&8547(94)ooo41-7
News on fundamental
reference data
PAUL B. FARNSWORTH Department of Chemistry, BrighamYoung University, Provo, UT 846024672, U.S.A. INTERNET:[email protected] (Received 9 May 1994)
THIS COLUMNwill
be a departure from the norm in that, rather than focusing my attention on the most recent work in the area of fundamental atomic reference data, I would like to devote most of the column to the long-term efforts of a single group, the Laser Spectroscopy Group at the CSIRO Division of Materials Science and Technology. The decision to do so is prompted by a feeling that my predecessor and I have been guilty of a degree of scientific provincialism. We have frequent contact with scientists in the United States and Western Europe, but much rarer interaction with scientists in other parts of the world. In past editions of this column we have ignored the important work by the Laser Spectroscopy Group at CSIRO that has spanned nearly two decades. This edition of the column is an attempt to correct that oversight and to bring to the attention of analytical spectroscopists a number of important contributions to the pool of fundamental data on atoms. The CSIRO Laser Spectroscopy Group was established in 1978 and built on the pioneering atomic absorption work of Sir ALAN WALSH and his colleagues. The Project Leader and Chief Research Scientist is Dr PETER HANNAFORD. Other permanent members of the group are: Senior Research Scientist DAVID GOUGH, Principal Research Scientists PETER LARKINS, MARTIN LOWE and RUSSELLMCLEAN, and Honorary Fellow Sir ALAN WALSH. The group is active in several areas related to the production of fundamental atomic data. These include: The use of cathodic sputtering as a universal means of producing atoms and singly charged atomic ions for subsequent study by time-resolved fluorescence and high-resolution Doppler-free laser spectroscopies. The time-resolved fluorescence spectroscopy is used in the determination of atomic lifetimes, absolute oscillator strengths, and Land6 g factors. The Doppler-free laser spectroscopy is used in the determination of hyperfine structures and isotope shifts of atomic resonance lines. The application of Doppler-free laser spectroscopy as a technique for the determination of isotopic abundances of elements. The development of diode lasers as high-resolution sources for atomic spectroscopy. Laser cooling and trapping of neutral atoms and the application of this technique to the development of an atom matter-wave interferometer. Over the past decade, the group has produced a series of reviews on work in the first area described above. Listed in chronological order, they are: Spectroscopy with sputtered atoms, Confemp. Phys. 24,251 (1983). and R. M. Lowe, Determination of atomic lifetimes using laserinduced fluorescence from sputtered metal vapor, Opt. Eng. 22, 532 (1983). 3. P. Hannaford, Laser spectroscopy beyond the sodium D lines, The Australian Physicist 23, 4 (1986). 4. P. Hannaford and R. M. Lowe, Some recent developments in atomic lifetime determinations, Aus?. J. Phys. 39, 829 (1986). 1. P. Hannford,
2. P. Hannaford
811
812
P. B. FARNSWORTH
5.
P. Hannaford and A. Walsh, Sputtered atoms in absorption and fluorescence spectroscopy, Spectrochim. Acta 43B, 1053 (1988). 6. P. Hannaford, Laser spectroscopy with sputtered atoms, Proceedings of the Ninth National Conference on Atomic and Molecular Physics, Bombay (1992), in press.
During the same time period the group has generated an impressive list of research papers. The papers dealing with fundamental atomic data are easily separated into two groups. The first group includes measurements of lifetimes, oscillator strengths and transition probabilities: 1. D. S. Gough, P. Hannaford and R. M. Lowe, Radiative lifetimes and oscillator strengths in neutral iridium, J. Phys. B: At. Mol. Phys 16, 785 (1983). 2. P. Hannaford and R. M. Lowe, Radiative lifetimes in MO II, J. Phys. B: At. Mol. Phys. 16, 4539 (1983). 3. P. Hannaford and R. M. Lowe, Radiative lifetimes in Fe II using selective laser excitation, J. Phys. B: At. Mol. Phys. 16, L43 (1983). 4. E. Biemont, N. Grevesse, P. Hannaford, R. M. Lowe and W. Whaling, A redetermination of the solar abundance of molybdenum, Astrophys. J. 275, 889 (1983). 5. W. Whaling, P. Hannaford, R. M. Lowe, E. BiCmont and N. Grevesse, Lifetimes, branching ratios and transition probabilities in MO I, J. Quunt. Spectrosc. Radiat. Transfer 32, 69 (1984). 6. P. Hannaford, R. M. Lowe, E. BiCmont and N. Grevesse,
Radiative lifetimes for Nb II and the problem of solar abundance of niobium, Asfron. Asfrophys. 143, 447 (1985). 7. P. Hannaford and R. M. Lowe, Radiative lifetimes of low-lying levels in Sm I, J. Phys. B: At. Mol. Phys. 18, 2365 (1985). 8. W. Whaling, P. Hannaford, R. M. Lowe, E. BiCmont and N. Grevesse, Absolute transition probabilities in vanadium I and solar abundance of vanadium, Asfron. Astrophys. 153, 109 (1985). 9. E. Biemont, N. Grevesse, P. Hannaford and R. M. Lowe, Lifetimes in Sm II and the solar abundance of samarium, Astron. Astrophys. 222, 307 (1989). 10. R. M. Lowe and P. Hannaford, Radiative lifetimes in Ti I, 2. Phys. D 21, 205 (1991). 11. P. Hannaford, R. M. Lowe, N. Grevesse and A. Noels, Lifetimes in Fe II and the solar abundance of Iron, As&on. Astrophys. 2J9, 301 (1992). 12. E. Biemont and R. M. Lowe, Radiative lifetime measurements in Dy II and the solar abundance of dysprosium, Astron. Astrophys. 273, 665 (1993). 13. R. M. Lowe, P. Hannaford and A.-M. Mktensson-Pendrill, Radiative lifetimes of the 6p2Pln and 6pzP,, levels in Yb II, 2. Phys. D 29, 39 (1994). The second group of papers includes the measurements isotope shifts by Doppler-free laser spectroscopy:
of hyperfhte splittings and
1. D. S. Gough and P. Hannaford, Very high resolution laser saturation spectroscopy in hollow-cathode and glow discharges, Optics Comm. 55, 91 (1985). 2. D. S. Gough, P. Hannaford, R. M. Lowe and A. P. Willis, Hyperfine structures in 51V using laser saturation spectroscopy in a hollow-cathode discharge, J. Phys. B: At. Mol. Phys. 18, 3895 (1985). 3. R. J. McLean, P. Hannaford, H.-A. Bachor, P. T. H. Fisk and R. J. Sandeman, Absorption line narrowing measurements of hyperfme structure in highly excited levels of yttrium, 2. Phys. D 1, 253 (1986). 4. D. S. Gough and P. Hannaford, High quality saturated absorption spectroscopy in a sputtered vapour: application to hyperfine structure in Zr I, Optics Comm. 67, 209 (1988). 5. P. Hannaford and D. S. Gough, High quality saturated absorption spectroscopy in a sputtered vapour: application to isotope shifts in Zr I, Laser Spectroscopy IX, Proceedings
of the Ninth International Conference
on Laser Spectroscopy,
News on fundamentalreference data
6.
7. 8. 9.
10. 11.
813
Eds M. S. Feld, J. E. Thomas and A. Mooradian, pp. 83-85. Academic Press, Boston (1989). A. W&utstriim, D. S. Gough and P. Hannaford, Hyperfine structure measurements in tantalum I using laser saturation spectroscopy in a sputtered vapour, 2. Phys. 22, 723 (1992). P. Hannaford, Hyperfine structure and isotope shifts in the 595.5nm (a3&-z5F1) ground-state transition in Zr I, Opt. Lett. 17, 432 (1992). P. L. Larkins and P. Hannaford, Precision energies and hyperfine structures of the 5~5p~P”~,i,~ and 5s 6r3S1 levels in II, 2. Phys. 27, 313 (1993). R. J. McLean, P. Hannaford, P. L. Larkins and W. J. Rowlands, Diode laser saturated absorption measurements of isotope shifts and hyperfine structure of Zr I, Optics Comm. 102, 43 (1993). A. Wgnnstriim, D. S. Gough and P. Hannaford, High resolution laser spectroscopy in yttrium ions in a sputtered vapour, Z. Phys. D 29, 39 (1994). A.-M. M&ensson-Pendrill, D. S. Gough and P. Hannaford, Isotope shifts and hypetfme structure in the 369.4 nm 6*&&j *PID resonance line of singly ionised ytterbium, Phys. Rev. A 49 (in press).
The consistently high level of productivity of the CSIRO laser group in the area of atomic reference data calls for continued attention to the group’s work by the analytical spectroscopic community. Other reference data news
In the previous two editions of this column [l, 21, I have made reference to the opacity project and its database, TOPbase. A limitation of that database that was not mentioned is that the f-values included in the database are for multiplets only, not for individual spectral lines. Data for individual lines can be readily calculated in cases of rigorous LS coupling. For many atoms, however, including C, N, and 0, such an approach can lead to large errors. WOLFGANGWIE~E at NIST has supplied me with references for calculated transition probabilities for those three elements that are done in intermediate coupling, and which provide data for individual lines of neutral carbon [3], nitrogen [4] and oxygen [5]. Since the last edition of the column, the Atomic Energy Level Data Center at NIST has published three volumes that will be of interest to the analytical spectroscopist. The first is a continuation of the series Selected Tables of Atomic Spectra begun by CHARLOTTE MOORE[6]. It is a compilation of energy levels and wavelengths for singly ionized oxygen (0 II). The second is a compilation of energy levels for all ionization stages of germanium (Ge I-Ge XXXII) [7]. In the final volume, JEAN GALLAGHERhas added to the legacy of CHARLOYTEMOORE by compiling under one cover Moore’s energy level and multiplet tables for hydrogen, carbon, nitrogen and oxygen atoms and ions [8]. With the exception of the 0 II data, the material in the tables has been published previously as sections of the series, Selected Tables of Atomic Spectra. The 0 II data were extracted from Ref. [6] above. Interest in solar abundances of iron-group elements continues to be a driving force for the generation of lifetime and wavelength data for those elements. Radiative lifetimes determined by laser-induced fluorescence and branching ratios determined by Fourier transform emission spectroscopy have been combined to determine the transition probabilities for 100 Ti II emission lines [9]. Transition probabilities for 550 Fe II lines have been determined from photographic solar spectra recorded on the Naval Research Laboratory normal incidence spectrometer aboard Skylab [lo]. Spectra from Fe hollow cathode lamps recorded on a combination of Fourier transform and grating instruments have been used to identify 86 new highly excited Fe I energy levels and to revise the energies of 110 previously reported levels [ll]. In a companion paper, 2200 lines from highly excited Fe I levels were identified, 1700 of which have been observed in the solar spectrum [12]. As a final note, a new set of calculations of energy levels and oscillator strengths for neutral calcium has recently been published [13]. The calculations are based on
814
P. B. FARNSWORTH
the configuration interaction method, and differ from previous calculations in that the Hamiltonian for the two valence electrons was modified by the addition of a semiempirical polarization potential. The results of the calculations are in better agreement with experiment than are previously reported theoretical values. REFERENCES [l] [2] [3] [4] [5] [6] [7] [8] [9] [lo] [ll] [12] [13]
P. B. Farnsworth, Specrroc~im. Acta 48B, 1301 (1993). P. B. Farnsworth, Spectrochim. Acta 48B, 1651 (1993). A. Hibbert, E. Bibmont, M. Godefroid and N. Vaeck, A&on. Astrophys. Suppl. Ser. 99, 179 (1993). A. Hibbert, E. BiCmont, M. Godefroid and N. Vaeck, Astron. Astrophys. Suppl. Ser. 88, 505 (1991). E. Bitmont, A. Hibbert, M. Godefroid, N. Vaeck and B. C. Fawcett, Astrophys. 1. 375, 818 (1991). W. C. Martin, V. Kaufman and A. Musgrove, J. Phys. Chem. Ref. Data 22, 1179 (1993). J. Sugar and A. Musgrove, J. Phys. Chem. Ref. Data 22, 1213 (1993). C. E. Moore, Tables of Spectra of Hydrogen, Carbon, Nitrogen, and Oxygen Atoms and Ions, Ed. J. W. Gallagher. CRC Press, Boca Raton, FL (1993). A. Bizzarri, M. C. E. Huber, A. Noels, N. Grevesse, S. D. Bergeson, P. Tsekeris and J. Lawler, Astron. Astrophys. 273, 707 (1993). J. 0. Ekberg and U. Feldman, Astrophys. J. Suppl. Ser. 86, 611 (1993). G. Nave and S. Johansson, Astron. Astrophys. 274, %l (1993). G. Nave and S. Johansson, Astron. Astrophys. Suppl. Ser. 102, 269 (1993). J. Miltroy, 1. Phys. B: At. Mol. Phys. 26, 3703 (1993).