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Fine structure splitting of the term 3s3p24P in Al-like ions
Volume 127, number 2
PHYSICS LETTERS A
8 February 1988
FINE STRUCTURE SPLITTING OF THE TERM 3s3p2 4P IN Al-LIKE IONS U. LITZEN and A. REDFORS Department of Physics, University ofLund, S-223 62 Lund, S~v eden Received 19 November 1987; revised manuscipt received 16 December 1987; accepted for publication 17 December 1987 Communicated by B. Fricke
Measured wavelengths of the multiplet 3s3p2 4P—3p3 4S in the Al I.like ions Ca VIII—Zn XVIII have been used for deriving the fine structure intervals of the “P term. These experimentally determined intervals have been compared with theoretical values from a multiconfiguration Dirac—Fock calculation.
Transitions from metastable states are important tools for diagnostics of low density plasmas, and numerous lines from such transitions have been identifled in both laboratory and astrophysical sources. Further information is, however, needed. In a recent work [1,2] the beam—foil method was used for obtaming wavelengths of spin-forbidden lines and lifetimes of metastable levels in high charge states of Ti, Fe, Ni and Cu. In the Al-like sequence it was noticed that the knowledge of the metastable 3s3p24P is sparse along the sequence. In order to facilitate the identification of the spin-forbidden lines from this term to the 3s23p2P ground term we have undertaken an investigation of the 4P intervals in Ca VIII—Zn XVIII. This work is part of a more comprehensive study of All-like ions. The fine structure of the 4P has been derived from the wavelengths of the multiplet 3s3p24P—3p34S. The spectra were emitted from laser-produced plasmas obtained by focusing high power pulses from a Quantel NG24 Nd:YAG/glass laser on flat targets of the pure elements. The laser emits 3 ns pulses, and we used pulse energies ranging from 2 J in calcium to 4 J in zinc. The plasma was viewed by the spectrograph in a direction parallel to the target plane and perpendicular to the main direction of the plasma expansion, thus minimizing the Doppler shift. The spectra were recorded with a 3 m normal incidence spectrograph using a 1200 grooves mm’ gold-coated grating. Ten to twenty laser pulses were sufficient to get well exposed spectrograms on Kodak 101 plates. 88
Recommended wavelengths of 3s—3p and 3p—3d transitions of sodium-like ions [3] and accurately measured 3—3 lines of aluminium- and silicon-like ions [4] together with the recently published wavelengths in magnesium-like spectra [5—81were used as wavelengths references. Due to possible shifts between references and measured lines caused by the charge dependent yelocity distribution of the plasma ions, the comparatively large line widths caused by Doppler effect, and perturbations from the background of unresolved weak lines we only state the absolute wavelengths accuracy to be better than ±0.02A. The intervals discussed in this paper are, however, determined as wavenumber differences of lines with small separations, which gives a considerably higher accuracy. Therefore the uncertainties of the intervals given in table 2 correspond to a relative wavelength uncertainty of ±0.01 A. The 3s3p24P—3p34S multiplet had been indentifled previously in a number of the elements discussed in the present work. References to previous measurements in Ca VIII—V XI, Mn XIII and Fe XIV are given in ref. [9]. Recent investigations of Cu XVII and Zn XVIII are reported in refs. [7,8]. In Sc IX—V XI, Mn XIII and Fe XIV the wavelengths have been improved in the present work. In Mn XIII, Fe XIV, Cu XVII and Zn XVIII additions and corrections regarding the J= 1/2—3/2 and 3/2—3/2 lines have been made. The observed wavelengths of the multiplet are presented in table 1. The isoelectronic
0375-9601/88/$ 03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
Volume 127, number 2
PHYSICS LETTERS A
Table I 2 4P—3p3 ‘5 used to Observed spectral lines of the multiplet 3s3p derive the fine structure splitting of the term “P in the configuration 3s3p2. The relative intensities of the lines are roughlyproportional to the statistical weights ofthe lower levels. p indicates that the wavelength may be perturbed by a nearly coincidingline, Spectrum
Wavelength (A) 1/2—3/2
Sc IX Ca VIII Ti X
3/2—3/2
417.462 b) 462.591 ~ 379.780’°
VXI Cr XII Mn XIII FeXIV Co XV NiXVI Cu XVII Zn XVIII
5/2—3/2
465.993~ 421.231 b)
426.855 47l.l83~ b)
383913b)
39o.ol6~
352334b)
358846b)
320.191 296.073 274.797 p255.828 238.699 223.181 208.994
325.177 p 301.525 280.739 262.249 245.671 230.675~ 2l7.o66”~
332.126 308.895”~ 288.512~ 270.378 254.139 239.462~ 226.079 ~)
~ Wavelengths are from ref. [14]. b The transition has been previously identified by Fawcett as referenced in ref. [9]. Wavelengths from refs. [7,8], correctedaccording to ref. [6]. d) Wavelength from ref. [8], where the transition is identified as belonging to Zn XVII.
1I I ~. 1.225) (10’ cm
3s3p2 4P
graphs like those shown in fig. 1. The lines are also easily followed on the photographic plates throughout the sequence since they are situated around the Mg I-like resonance line 3~2 ‘S 0—3s3p ‘P1. To get a finer tuned instrument for the identifications we have also studied the discrepancies 24P fine between structurean andabour initio excalculation of the 3s3p perimentally derived values. The theoretical results were obtained by Huang [10] from a multi-configuration Dirac—Fock (MCDF) calculation with the Desclaux code. Several other calculations of aluminium-like systems have been published [11—13],but only the work by Huang comprises all the elements we have investigated. As can be seen in fig. 2 the differences between the observed and calculated 1/2—3/2 and 3/2—5/2 intervals vary smoothly along the sequence. It was found that the intervals 1/2—3/2 in Cu XVII and 3/2—5/2 in Zn XVIII derived from refs. [7,8] deviate from the smooth trend, and the values for these points shown in the figures involve some newly identified lines reported in table 1. The trends in the figures indicate that the discrepancies between theory and observaMCDF calculation, where the agreement for the fine structure should be improved at high Z where the relativistic effects have a larger influence. It should,
I _______
24
trend the wavenumbers is shownofin fig. 1. The of preliminary identifications previously unknown lines were made by means of isoelectronic
~
p347.787~°
25
8 February 1988
-
3p3 ~
1~I2
~~I2
Table structure tions 2increase with of Z. the This not expected from an Fine splitting termis 3s3p2 “P. The uncertainties A, except for lines marked p in table 1 where the estimated uncertainty is ±0.02 A.
are derived Spectrum from an estimated Energyerror splitting in the(cm—’) wavelengths of ±0.01 1/2—3/2
~
• CaVIII Ti X Cr XII Fe XIV Ni,XVI ThXVII1~ I I I I I I I I XVII ScIX VXI MnXIII CoXV CuXVII Fig. 1. Isoelectronic evolution of the wavenumbers of the 3s3p24P—3p34S multiplet. •
3/2—5/2
Ca VIII ScIX TiX VXI CrXII MnXIII
1578(10) 2143(11) 2835(20) 3711(24) 4789(19) 6107(21)
2364 (10) 3128(11) 4076(20) 5151(15) 6434(19) 7913(21)
Fe XIV CoXV Ni XVI
7710(22) 9571 (45) 11881(34)
9596(25) 11471(29) 13579 (32)
Cu XVII Zn XVIII
14555(40) 17793(44)
15908(36) 18366(41)
89
Volume 127, number 2 ~~
I
PHYSICS LETTERS A
I
I
I
I
I
I
I
I
1,~I
~Ee~Ec
1cm
180
8 February 1988 I
I
(C.1)
1)
I
a
I
I
I
I
I
11
(10’ cm”
3s23p2P 60
16
-60
15
3s3p24P
1/2
3/2
3/2—5/2 60
14
-60~
3/2—1/2
—180
—300
,
XVII
CaVIII
,
Sc IX
Ti,X I
VXI
Cr,XII
Fe,XIV I Ni,XVI ZnXVIII MnXIII CoXV CuXVII I
Fig. 2. The differences between the experimentally determined and theoretically predicted 3s3p2 “P fine structure splitting J= 1/2—3/2 and 3/2—5/2 in the elements K—Zn. The error bars correspond to an uncertainty of ±0.01 A in the wavelengths for all the transitions except those marked i in table 1, where the estimated uncertainty is ±0.02 A.
however, be noticed that the relative deviations are less serious, as the fine structure increases rapidly with Z. A cause for the absolute deviations may be that the J= 1/2 and 5/2 levels of the 4P are mixed with 2S and 2D respectively, while the eigenvector of J= 3/2 shows a high purity. This mixing is of course of relativistic (spin—orbit) origin and becomes more and more significant along the sequence since the spin—orbit integral increases with the fourth power of Z. As the energy shift caused by the mixing is determined both by the spin—orbit interaction and the electrostatic term distances, an error in the latter is strongly magnified by the increasing spin—orbit integral. The beam—foil study [1,2] of the spin-forbidden 3s23p 2P—3s3p2“P yielded wavelengths for a number of lines in Ti X, Fe XIV, Ni XVI and Cu XVII. The isoelectronic trend of the wavenumbers is shown in fig. 3, where also the data for Ar VI reported in ref. [14] are included. The wavelength accuracy and the number of experimental data points is not sufficient to allow accurate inter- or extrapolation of wave90
13 ArVI I
I
I
I
I X
I
I
I
I
FeXIV
I
I
NiXVICu XVII
Fig. 3. Isoelectronic evolution of the wavenumbers of the spinforbidden 3s33p 2P—3s3p2“P transition in Ar VI—Cu XVII.
lengths. The least-squares-fitted curve in the figure shows, however, the smooth isoelectronic trend within the experimental error limits. Tentative identifications of the J= 1/2—1/2 transition in Se XXII, Mo XXX and Ag XXXV in a tokamak plasma have recently been reported by Hinnov et al. [15]. Due to the bad statistics of the fit an extrapolation of the curve in fig. 3 cannot be used to test if these identifications are compatible with the measurements in refs. [1,2]. A more thorough investigation of the spectra and energy levels of aluminium-like elements is in progress.
This work was supported by the Swedish Natural Science Research Council and the Swedish Energy Research Commision.
References [1] E. Träbert, R. Hutton and I. Martinson, Z. Phys. D 5 (1987) 125. [2] E. Träbert, R. Hutton and I. Martinson, Mon. Not. R. Astron. Soc. 227 (1987) 27P.
Volume 127, number 2
PHYSICS LETTERS A
[3] J. Reader, V. Kaufman, J. Sugar, J.O. Ekberg, U. Feldman, CM. Brown, J.F. Seely and W.L. Rowan, J. Opt. Soc. Am. B, to be published. [4] R. Smitt, L.A. Svensson and M. Outred, Phys. Scr. 13 (1976) 293. [5] S.S. Churilov, E.Ya. Kononov, A.N. Ryabtsev and Yu.F. Zayikin, Phys. Scr. 32 (1985) 501. [6] J. Sugar and V. Kaufman, private communication; J. Opt. Soc. Am. B, to be published. [7] J. Sugar and V. Kaufman, J. Opt. Soc. Am. B 3 (1986) 704. [8] J. Sugar and V. Kaufman, Phys. Scr. 34 (1986) 797 [9] J. Sugar and C. Corliss, J. Phys. Chem. Ref. Data 14, suppl.
8 February 1988
[101 K.N. Huang, At. Data NucI. Data Tables 34 (1986) 1. [11] B.C. Fawcett, At. Data NucI. Data Tables 28 (1983) 557. [12] C. Froese-Fischer and B. Liu, At. Data Nucl. Data Tables 34 (1986) 261. [131 A. Farrag, E. Luc-Koenig and J. Sinzelle, At. Data NucI. Data Tables 27 (1982) 539. [14] JO. Ekberg and L.A. Svensson, Phys. Scr. 2 (1970) 283. [15] E. Hinnov, F. Boody, S. Cohen, U. Feldman, J. Hosea, K. Sato, J.L. Schwob, S. Suckewer and A. Wouters, J. Opt. Soc. Am. B 3(1986)1288.
2 (1985).
91
PHYSICS LETTERS A
8 February 1988
FINE STRUCTURE SPLITTING OF THE TERM 3s3p2 4P IN Al-LIKE IONS U. LITZEN and A. REDFORS Department of Physics, University ofLund, S-223 62 Lund, S~v eden Received 19 November 1987; revised manuscipt received 16 December 1987; accepted for publication 17 December 1987 Communicated by B. Fricke
Measured wavelengths of the multiplet 3s3p2 4P—3p3 4S in the Al I.like ions Ca VIII—Zn XVIII have been used for deriving the fine structure intervals of the “P term. These experimentally determined intervals have been compared with theoretical values from a multiconfiguration Dirac—Fock calculation.
Transitions from metastable states are important tools for diagnostics of low density plasmas, and numerous lines from such transitions have been identifled in both laboratory and astrophysical sources. Further information is, however, needed. In a recent work [1,2] the beam—foil method was used for obtaming wavelengths of spin-forbidden lines and lifetimes of metastable levels in high charge states of Ti, Fe, Ni and Cu. In the Al-like sequence it was noticed that the knowledge of the metastable 3s3p24P is sparse along the sequence. In order to facilitate the identification of the spin-forbidden lines from this term to the 3s23p2P ground term we have undertaken an investigation of the 4P intervals in Ca VIII—Zn XVIII. This work is part of a more comprehensive study of All-like ions. The fine structure of the 4P has been derived from the wavelengths of the multiplet 3s3p24P—3p34S. The spectra were emitted from laser-produced plasmas obtained by focusing high power pulses from a Quantel NG24 Nd:YAG/glass laser on flat targets of the pure elements. The laser emits 3 ns pulses, and we used pulse energies ranging from 2 J in calcium to 4 J in zinc. The plasma was viewed by the spectrograph in a direction parallel to the target plane and perpendicular to the main direction of the plasma expansion, thus minimizing the Doppler shift. The spectra were recorded with a 3 m normal incidence spectrograph using a 1200 grooves mm’ gold-coated grating. Ten to twenty laser pulses were sufficient to get well exposed spectrograms on Kodak 101 plates. 88
Recommended wavelengths of 3s—3p and 3p—3d transitions of sodium-like ions [3] and accurately measured 3—3 lines of aluminium- and silicon-like ions [4] together with the recently published wavelengths in magnesium-like spectra [5—81were used as wavelengths references. Due to possible shifts between references and measured lines caused by the charge dependent yelocity distribution of the plasma ions, the comparatively large line widths caused by Doppler effect, and perturbations from the background of unresolved weak lines we only state the absolute wavelengths accuracy to be better than ±0.02A. The intervals discussed in this paper are, however, determined as wavenumber differences of lines with small separations, which gives a considerably higher accuracy. Therefore the uncertainties of the intervals given in table 2 correspond to a relative wavelength uncertainty of ±0.01 A. The 3s3p24P—3p34S multiplet had been indentifled previously in a number of the elements discussed in the present work. References to previous measurements in Ca VIII—V XI, Mn XIII and Fe XIV are given in ref. [9]. Recent investigations of Cu XVII and Zn XVIII are reported in refs. [7,8]. In Sc IX—V XI, Mn XIII and Fe XIV the wavelengths have been improved in the present work. In Mn XIII, Fe XIV, Cu XVII and Zn XVIII additions and corrections regarding the J= 1/2—3/2 and 3/2—3/2 lines have been made. The observed wavelengths of the multiplet are presented in table 1. The isoelectronic
0375-9601/88/$ 03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
Volume 127, number 2
PHYSICS LETTERS A
Table I 2 4P—3p3 ‘5 used to Observed spectral lines of the multiplet 3s3p derive the fine structure splitting of the term “P in the configuration 3s3p2. The relative intensities of the lines are roughlyproportional to the statistical weights ofthe lower levels. p indicates that the wavelength may be perturbed by a nearly coincidingline, Spectrum
Wavelength (A) 1/2—3/2
Sc IX Ca VIII Ti X
3/2—3/2
417.462 b) 462.591 ~ 379.780’°
VXI Cr XII Mn XIII FeXIV Co XV NiXVI Cu XVII Zn XVIII
5/2—3/2
465.993~ 421.231 b)
426.855 47l.l83~ b)
383913b)
39o.ol6~
352334b)
358846b)
320.191 296.073 274.797 p255.828 238.699 223.181 208.994
325.177 p 301.525 280.739 262.249 245.671 230.675~ 2l7.o66”~
332.126 308.895”~ 288.512~ 270.378 254.139 239.462~ 226.079 ~)
~ Wavelengths are from ref. [14]. b The transition has been previously identified by Fawcett as referenced in ref. [9]. Wavelengths from refs. [7,8], correctedaccording to ref. [6]. d) Wavelength from ref. [8], where the transition is identified as belonging to Zn XVII.
1I I ~. 1.225) (10’ cm
3s3p2 4P
graphs like those shown in fig. 1. The lines are also easily followed on the photographic plates throughout the sequence since they are situated around the Mg I-like resonance line 3~2 ‘S 0—3s3p ‘P1. To get a finer tuned instrument for the identifications we have also studied the discrepancies 24P fine between structurean andabour initio excalculation of the 3s3p perimentally derived values. The theoretical results were obtained by Huang [10] from a multi-configuration Dirac—Fock (MCDF) calculation with the Desclaux code. Several other calculations of aluminium-like systems have been published [11—13],but only the work by Huang comprises all the elements we have investigated. As can be seen in fig. 2 the differences between the observed and calculated 1/2—3/2 and 3/2—5/2 intervals vary smoothly along the sequence. It was found that the intervals 1/2—3/2 in Cu XVII and 3/2—5/2 in Zn XVIII derived from refs. [7,8] deviate from the smooth trend, and the values for these points shown in the figures involve some newly identified lines reported in table 1. The trends in the figures indicate that the discrepancies between theory and observaMCDF calculation, where the agreement for the fine structure should be improved at high Z where the relativistic effects have a larger influence. It should,
I _______
24
trend the wavenumbers is shownofin fig. 1. The of preliminary identifications previously unknown lines were made by means of isoelectronic
~
p347.787~°
25
8 February 1988
-
3p3 ~
1~I2
~~I2
Table structure tions 2increase with of Z. the This not expected from an Fine splitting termis 3s3p2 “P. The uncertainties A, except for lines marked p in table 1 where the estimated uncertainty is ±0.02 A.
are derived Spectrum from an estimated Energyerror splitting in the(cm—’) wavelengths of ±0.01 1/2—3/2
~
• CaVIII Ti X Cr XII Fe XIV Ni,XVI ThXVII1~ I I I I I I I I XVII ScIX VXI MnXIII CoXV CuXVII Fig. 1. Isoelectronic evolution of the wavenumbers of the 3s3p24P—3p34S multiplet. •
3/2—5/2
Ca VIII ScIX TiX VXI CrXII MnXIII
1578(10) 2143(11) 2835(20) 3711(24) 4789(19) 6107(21)
2364 (10) 3128(11) 4076(20) 5151(15) 6434(19) 7913(21)
Fe XIV CoXV Ni XVI
7710(22) 9571 (45) 11881(34)
9596(25) 11471(29) 13579 (32)
Cu XVII Zn XVIII
14555(40) 17793(44)
15908(36) 18366(41)
89
Volume 127, number 2 ~~
I
PHYSICS LETTERS A
I
I
I
I
I
I
I
I
1,~I
~Ee~Ec
1cm
180
8 February 1988 I
I
(C.1)
1)
I
a
I
I
I
I
I
11
(10’ cm”
3s23p2P 60
16
-60
15
3s3p24P
1/2
3/2
3/2—5/2 60
14
-60~
3/2—1/2
—180
—300
,
XVII
CaVIII
,
Sc IX
Ti,X I
VXI
Cr,XII
Fe,XIV I Ni,XVI ZnXVIII MnXIII CoXV CuXVII I
Fig. 2. The differences between the experimentally determined and theoretically predicted 3s3p2 “P fine structure splitting J= 1/2—3/2 and 3/2—5/2 in the elements K—Zn. The error bars correspond to an uncertainty of ±0.01 A in the wavelengths for all the transitions except those marked i in table 1, where the estimated uncertainty is ±0.02 A.
however, be noticed that the relative deviations are less serious, as the fine structure increases rapidly with Z. A cause for the absolute deviations may be that the J= 1/2 and 5/2 levels of the 4P are mixed with 2S and 2D respectively, while the eigenvector of J= 3/2 shows a high purity. This mixing is of course of relativistic (spin—orbit) origin and becomes more and more significant along the sequence since the spin—orbit integral increases with the fourth power of Z. As the energy shift caused by the mixing is determined both by the spin—orbit interaction and the electrostatic term distances, an error in the latter is strongly magnified by the increasing spin—orbit integral. The beam—foil study [1,2] of the spin-forbidden 3s23p 2P—3s3p2“P yielded wavelengths for a number of lines in Ti X, Fe XIV, Ni XVI and Cu XVII. The isoelectronic trend of the wavenumbers is shown in fig. 3, where also the data for Ar VI reported in ref. [14] are included. The wavelength accuracy and the number of experimental data points is not sufficient to allow accurate inter- or extrapolation of wave90
13 ArVI I
I
I
I
I X
I
I
I
I
FeXIV
I
I
NiXVICu XVII
Fig. 3. Isoelectronic evolution of the wavenumbers of the spinforbidden 3s33p 2P—3s3p2“P transition in Ar VI—Cu XVII.
lengths. The least-squares-fitted curve in the figure shows, however, the smooth isoelectronic trend within the experimental error limits. Tentative identifications of the J= 1/2—1/2 transition in Se XXII, Mo XXX and Ag XXXV in a tokamak plasma have recently been reported by Hinnov et al. [15]. Due to the bad statistics of the fit an extrapolation of the curve in fig. 3 cannot be used to test if these identifications are compatible with the measurements in refs. [1,2]. A more thorough investigation of the spectra and energy levels of aluminium-like elements is in progress.
This work was supported by the Swedish Natural Science Research Council and the Swedish Energy Research Commision.
References [1] E. Träbert, R. Hutton and I. Martinson, Z. Phys. D 5 (1987) 125. [2] E. Träbert, R. Hutton and I. Martinson, Mon. Not. R. Astron. Soc. 227 (1987) 27P.
Volume 127, number 2
PHYSICS LETTERS A
[3] J. Reader, V. Kaufman, J. Sugar, J.O. Ekberg, U. Feldman, CM. Brown, J.F. Seely and W.L. Rowan, J. Opt. Soc. Am. B, to be published. [4] R. Smitt, L.A. Svensson and M. Outred, Phys. Scr. 13 (1976) 293. [5] S.S. Churilov, E.Ya. Kononov, A.N. Ryabtsev and Yu.F. Zayikin, Phys. Scr. 32 (1985) 501. [6] J. Sugar and V. Kaufman, private communication; J. Opt. Soc. Am. B, to be published. [7] J. Sugar and V. Kaufman, J. Opt. Soc. Am. B 3 (1986) 704. [8] J. Sugar and V. Kaufman, Phys. Scr. 34 (1986) 797 [9] J. Sugar and C. Corliss, J. Phys. Chem. Ref. Data 14, suppl.
8 February 1988
[101 K.N. Huang, At. Data NucI. Data Tables 34 (1986) 1. [11] B.C. Fawcett, At. Data NucI. Data Tables 28 (1983) 557. [12] C. Froese-Fischer and B. Liu, At. Data Nucl. Data Tables 34 (1986) 261. [131 A. Farrag, E. Luc-Koenig and J. Sinzelle, At. Data NucI. Data Tables 27 (1982) 539. [14] JO. Ekberg and L.A. Svensson, Phys. Scr. 2 (1970) 283. [15] E. Hinnov, F. Boody, S. Cohen, U. Feldman, J. Hosea, K. Sato, J.L. Schwob, S. Suckewer and A. Wouters, J. Opt. Soc. Am. B 3(1986)1288.
2 (1985).
91