Spectrum and energy levels of ten-times ionized yttrium(Y xi)

Joseph Reader and Nicolo AcquistaNational Bureau of Standards, Washington, D. C. 20234

(Received 19 March 1979)

The spectrum of Y xi was observed with a low-inductance vacuum spark and a laser-producedplasma in the region from 70 to 630 A on the 10.7-m grazing-incidence spectrograph at NBS. Fromthe identification of 40 lines, a system of 29 energy levels was determined. The level system (Cu iiisoelectronic sequence, 3d '0n1) includes the series ns (n = 4-7), np (n = 4-6), nd (n = 4-6),nf(n = 4-7), and ng (n = 5-8). The 4f 2 F term is inverted. The observed energy levels are comparedwith Hartree-Fock calculations. The ionization energy is determined from the ng series (n =5-8)to be 1 660 000 i 200 cm-' (205.82 i 0.03 eV).

Spectra of ions in the Cu I isoelectronic sequence haveseen increased interest lately because of their role in the di-agnosis of controlled fusion plasmas.l Recently we published 2

an extensive analysis of the spectrum of the copper-like ionMo XIV. The present paper is a similar analysis for the cop-per-like ion Yxi.

The first line identifications for Y XI were given by Alex-ander, Even-Zohar, Fraenkel, and Goldsmith.3 They useda vacuum spark to observe six lines of the type 4s -5p, 4p -5d,and 4p-5s lying in the region 117-179 A. In 1977 the presentauthors 4 identified the 4s-4p resonance lines, also by use ofa vacuum spark. In the present work we used a vacuum sparkand a laser-produced plasma to carry out a relatively completespectral analysis of this ion. Some 40 lines, representingtransitions between 29 energy levels, were identified.

EXPERIMENT

Our spark source was a low-inductance, three electrodetype, essentially the same as described by Feldman, Swartz,and Cohen.5 We used capacitors of either 4.7 or 14.2 MF atvoltages varying between 1 and 15 kV. The spectrum of Yxiwas generally well developed at a voltage of 3 kV, with littleenhancement at higher voltages.

The laser-produced plasma was obtained by focusing thelight from an Nd/glass laser (wavelength 1.06 ,im) onto flatmetallic targets. Typical laser pulses had an energy of 15 Jand a duration 10 ns. The spectrum of Y XI could be en-hanced relative to spectra of higher stages of ionization byusing laser pulses of greater energy and longer duration,typically 30 J in 20 ns.

The spectra were photographed on our 10.7-m grazing in-cidence spectrograph at an angle of incidence of 80°. Thegrating had 1200 lines/mm, providing a plate factor of 0.25A/mm at 300 A. The region covered was 70-630 A. Wave-length calibration in the region around 100 A was obtainedfrom a vacuum spark of Ti.6 At longer wavelengths, cali-bration was obtained from lines of YIV-vI measured previ-ously with sliding spark sources,7 -9 as well as impurity linesof oxygen and fluorine.10-13

All wavelength measurements were taken from observationswith the low-inductance spark, the laser-produced plasmabeing used primarily to distinguish stages of ionization.Further details concerning our experimental procedure aregiven in Ref. 2.

1285 J. Opt. Soc. Am., Vol. 69, No. 9, September 1979

LINE IDENTIFICATIONS, WAVELENGTHS, ENERGYLEVELS

The wavelengths, intensities, and classifications of theobserved lines of Y xi are given in Table I. The uncertainty

TABLE 1. Observed lines of Yxi. Symbols: h-hazy, p-perturbed byclose line.

x(A)

87.50387.80192.20693.81698.00799.76399.828

110.054112.357115.024115.406117.328118.375126.348129.176129.389130.421130.914152.726158.260158.981159.227167.630168.438169.186173.693179.504202.885292.893295.372299.507302.775302.820311.451327.516330.620349.013352.564479.770526.841

Int.

8050102530705

1001502025

100070015030050508020 h15

10045

15030080 h

30005000400 h100

1000600900900

500060001500 p1200 p3000

200008000

a (cm-1 )

1 142 820113894010845301065920102034010023801001720

908645890020869384866506852 311844773791465774138772863766748763860654767631872629006628034596552593690591065575728557091492890341422338556333882330278.3330 229.2321077.8305328.6302462.0286522.3283636.4208433.2189810.6

Classification

4s 2S 1/2 - 6p 2P3/24s 2S1 /2 -6p 2P1 /2

4 p 2P1 /2- 7S 2S 1 /24p 2P3/2-7s 2S 1 ,24p 2P1/2-6d 2D3/24 p 2 P3/2- 6d 2D5/24p 2P3/2 -6d 2D3/24p 2P1/2-6s 2S ,'24 p 2P3/2-6s 2S1 ,24d 2D3/2 - 7f 2F5/24d 2D5/2-7f 2F7 /24s 2S 1 2 -5p 2 P3 /24s 2S,12-5p 2P1/24p 2p1/2 -5d 2D 3/24p 2P3,2 - 5d 2D5/24 p 2P3/2-5d 2D3/24d 2D3/2-6f/ F5/24d 2D5/2-6f 2F7/2

4f2F-8g2G4d 2D3/2 - 6p 2P3 /24d 2D5/2-6p 2P3/24d 2D3/2 -6p 2p 1/24d 2D3/2-5f 2F5/24d 2D5/2 - 5f 2F7 /2

4f2F-7g2G4p 2P,- 5s 2S 1 /,24p 2P3 /2-5s 2S1,2

4f 2F- 6g'2G4d 2D3/2- 5p 2P3/24d 2D 5/2- 5p 2 P3 /24d 2D3/2-5p 2P1/24f 2F7/2-5g 2G/24f 2F5/2-5g 2G7 /24p 2P1 / 2-4d 2D3/24p 2P3/2-4d 2D.5/24p 2P3/ 2-4d 2D3/24d 2D3/2-4f 2F5/24d 2D5/2 -4f2 F7/24s 2S/,2-4p 2P3 /24s 2S1,2-4p 2P,/2

1285

TABLE 11. Energy levels of Y xl.

Term

4s 2 S

4p 2p

J1/2

1/23/2

4d 2D 3/25/2

E(cm-')

0

189811208433

Unc(cm-1)

2

33

Fine-structureinterval(cm-')n*

2.8282

3.00533.0245

510893 3 3.3993513761 4 3.4035

5s 2S 1/2 765531 13 3.8529

4f 2 F 7/25/2

5p 2p 1/23/2

5d 2D 3/25/2

797397 6 3.9234797415 5 3.9234

844775 6 4.0358852316 5 4.0546

981286 23982571 30

4.42314.4273

18622

2868

-18

7541

1285

6s 2S 1/2 1098454 29 4.8627

5f 2F 5/27/2

5g 2G 7/29/2

6p 2p 1/23/2

6d 2D 3/25/2

1 1074451107451

1 1276441127675

1 1389281 142768

12101511210809

1818

78

1914

3650

4.90214.9021

4.99424.9944

5.04805.0667

5.43295.4370

6

31

3 840

658

7s 2S 1/2 1274344 41 5.868

6f 2F 7/25/2

1277 621 29 5.8931 277 641 30 5.893

-20

6g2 G

7f 2F

7g 2G

8g 2G

Limit

7/2,9/2 1290295

7/2 13802675/2 1380277

7/2,9/2 1388470

7/2,9/2 1452172

1660000

13

3838

18

5.993

6.8906.890

6.993

22 7.993

of the wavelengths is :0.005 A. The intensities are visualestimates of photographic blackening.

The line at 202.885 A coincides with a line of 0 IV at thiswavelength. However, from the observed intensities of otherlines of 0 IV in this region, we conclude that the 0 IV line at202.885 A should not be present with sufficient intensity onthe present plates to seriously affect the Y XI line.

TABLE lll. Wavelengths of selected Yxa lines as calculated from optimizedlevel values.

A(A) Uncertainty (A)

87.5068 0.001187.8019 0.0015

117.3274 0.0007118.3747 0.0009

1286 J. Opt. Soc. Am., Vol. 69, No. 9, September 1979

The energy levels are given in Table II. They are plottedwith the observed transitions in Fig. 1. The level values and

10 their uncertainties were determined by a least-squares opti-mization procedure that minimizes the differences betweenthe observed and calculated wave numbers.1 4

The analysis of the spectrum was similar to our analysis ofMo XIV, as described in Ref. 2. In particular, the 4p-4d and

TABLE V. Values for the ionization energy of Y xi determined from variousseries. The adopted value of the ionization energy is 1 660000 ± 200cm'.

Quantum defectSeries formula Limit (cm-1 )

4s -6s linear 16594305s -7s linear 16599304s -7s quadratic 1660040

4p-6p linear 1659140

4d-6d linear 1659050

4f-6f linear 16611905f-7f linear 16609104f-7f quadratic 1660800

5g-7g linear 16602906g-8g linear 16600605g-8g quadratic 1659940

Joseph Reader and Nicolo Acquista 1286

TABLE IV. Energy parameters in cm- for Y xl.

Para- Ohs./ Obs.-Config. nieter I-IF Obs. HIF IIF

4s Eav 0 05s Eav 743879 765531 216526s Eav 1068744 1098454 297107s Eav 1241718 1274344 32626

4p Ea, 182576 202226 19650¢4p 10973 12415 1.131

5p Eav 820094 849802 29708* 5p 4456 5027 1.128

6 p Eav 1108334 1141488 33154tsp 2 279 2 560 1.123

4d Eav 481091 512613 315225id 1084 1 147 1.058

5d Eav 947 707 982 057 34 350t5d 488 514 1.053

6d Eav 1 175326 1210546 35 220

t6d 2.64 263 0.997

4f Eav 765051 797405 32 354

'If 505f Eav 1072320 1 107 448 35 128

¢5'f 306f Eav 1242364 1277630 35 266

ts6f 187f Ea, 1344539 1380271 35 732

,7f 12

5g Eav 1091020 1 127661 36 641N 8 7 0.9

6g E., 1253597 1290295 36 698

t6g 57g Eav 1351445 1388470 37 025

{7g 3

1200

E

C.D

CDCD

caLU

800

400

0

ns np nd nf ng

4d-4f transitions were identified with the aid of calculationsdue to Weiss.15 Our experimental 4p-4d wavelengths of311.451, 327.516, and 330.620 A compare to Weiss's calculatedvalues of 314.1, 328.5, and 331.6 A. Our 4d-4f wavelengthsof 349.013 and 352.564 A compare to Weiss's values of 350.1and 353.4 A.

The fine-structure intervals of the observed terms are givenin Table II. For the np and nd terms these intervals are ex-tremely regular. The values of rn* = n*(j=1+1/2) -n*(J=I-1/2) of the 4p, 5p, and 6p 2P terms are 0.0192,0.0188,and 0.0187, respectively. For the 4d, 5d, and 6d 2D terms thevalues of 5n* are 0.0042, 0.0042, and 0.0041, respectively.

Of some interest is the 4f 2F interval. This has a value of

-18 cm-1, compared to a nonrelativistic Hartree-Fock (HF)value of +175 cm- 1. This is similar to an anomaly 2 in MoXIV,where the observed 4f

2F interval is 118 cm-', compared to anonrelativistic HF value of 488 cm-1 . In Ref. 2 we suggestedthat the Mo XIV anomaly was due to a large corepolarization(correlation) effect for the 4f configuration. We now notethat, according to Luc-Koenig,16 such fine-structure anomaliesin one-electron spectra may be viewed as being due either tocorrelation effects or to relativistic effects, there being littledistinction between these two phenomena for this type ofspectrum. Indeed, the recent calculations of Cheng andKim,17 which are fully relativistic and do not include corre-lation effects, account rather well for the observed 2F intervals.Their calculations cover the n =4-6 configurations of 24 cop-per-like ions from Ge Iv to Pb LIV. The 4f 2F intervals that

1287 J. Opt. Soc. Am., Vol. 69, No. 9, September 1979

FIG. 1. Grotrian diagram for Yxi.Wavelengths are in A. Intensitiesare indicated in parentheses fol-lowing the wavelengths. Wave-lengths of the 4s-5p and 4s-6ptransitions are those calculatedfrom the optimized level values.

they obtain for Yxi and Mo XIV are -41 cm-1 and +78 cm-',respectively.

Although the fine-structure intervals of the 5f, 6f, and 7fconfigurations cannot be well determined experimentally, theobserved values are again noticeably smaller than the non-relativistic HF values. If the wavelengths of two 4d-nftransitions observed for each n/ 2F term are measured relativeto each other to an accuracy of ±0.003 A, the observed inter-vals are +6 ± 11 cm-' for 5/, -20 + 18 cm-' for 6f, and -10i 23 cm-1 for 7f. The nonrelativistic HF values for theseconfigurations are +105, +63, and +42 cm-1, respectively.The relativistic values of Cheng and Kim17 are -9 cm-' for5f and + 2 cm-' for 6f.

As shown in Table I, the intensities of the two observed4f-5g transitions (302.775 and 302.820 A) are about equal.This means that their classifications might possibly be in-terchanged. The present assignments imply a 5g 2G intervalof +31 cm-1, compared to a nonrelativistic HF value of +36cm-1 and a relativistic HF value' 7 of +29 cm-1. An inter-change of assignments would imply a 5g

2G interval of -67cm-1 . In MoxIv the collapsed 4f-5g multiplet implies thatthe 5g 2G interval there is approximately equal to the 4f/2F

interval, or about +100 cm-1. The nonrelativistic and rela-tivistic17 HF values there are +93 and +77 cm-', respectively.Thus, a negative 5g 2G interval in Y XI would be most un-likely.

The higher ng levels are all established by single lines.

Joseph Reader and Nicolo Acquista 1287

These lines have a hazy appearance that easily distinguishesthem. Their hazy appearance undoubtedly results from Starkbroadening of the ng levels.

In Table III we list the wavelengths calculated from theoptimized energy levels for the 4s-5p and 4s-6p transitions.The small uncertainties of the calculated values make themsuitable as Ritz-type standards.

In Table IV we give the nonrelativistic Hartree-Fock valuesof the average energies and spin-orbit constants of all con-figurations from n = 4 to n = 7, as calculated with the com-puter program of Froese-Fischer.1 8 The observed values arealso given. The HF energies have been normalized to zero forthe 4s configuration. As in Mo XIv, the HF calculation yieldsgood relative energies, except for configurations that aregreatly affected by relativity. Since the ng-electrons are notsignificantly affected by relativity, we conclude that thebinding energy of the 4s electron is increased by about 37 000cm-' due to relativistic effects. The 4p, 5s, 5p, and 6s con-figurations are also significantly affected.

IONIZATION ENERGY

In Table V we list the values for the ionization energy ofY XI obtained from the various observed series. For the ion-ization energy, we adopt the value 1660000 cm-', which isvery nearly the limit of the four-member ns and ng series. Asin Mo XIV, the limit of the observed nf series is slightly higherthan the limit of the ng series. The difference in Y XI is 0.05%.If comparable series are considered, the percentage differencesin Y XI and MoXIV are nearly the same. From the consis-tency of the values in Table V and the uncertainty of the levelvalues, we estimate the uncertainty of the limit to be +200cm-'. The ionization energy of YXI is thus 1660000 +200cm-l (205.82 + 0.03 eV).

ACKNOWLEDGMENTS

The spectrograms of the laser-produced plasma were madein cooperation with G. Luther. We would like to thank A.Weiss for predicting the 4p-4d and 4d-4f transitions for us.This work was supported in part by the Office of MagneticFusion Energy of the U.S. Department of Energy.

1E. Hinnov, "Highly ionized atoms in tokamak discharges," Phys.Rev. A 14,1533-1541 (1976).

2J. Reader, G. Luther, and N. Acquista, "Spectrum and energy levelsof thirteen-times ionized molybdenum (Moxiv)," J. Opt. Soc. Am.69, 144-149 (1979).

3 E. Alexander, M. Even-Zohar, B. S. Fraenkel, and S. Goldsmith,"Classification of Transitions in the euv Spectra of YIX-XIII,Zrx-xiv, NbxI-xv, and Moxii-xvI," J. Opt. Soc. Am. 61, 508-514(1971).

4J. Reader and N. Acquista, "4s-4p Resonance Transitions in HighlyCharged Cu- and Zn-like Ions," Phys. Rev. Lett. 39, 184-187(1977).

5 U. Feldman, M. Swartz, and L. Cohen, "Vacuum UltravioletSource," Rev. Sci. Instrum. 38, 1372-1373 (1967).

6L. A. Svensson and J. 0. Ekberg, "The titanium vacuum-sparkspectrum from 50 to 425 A," Ark. Fys. 40, 145-164 (1969).

7J. Reader, G. L. Epstein, and J. 0. Ekberg, "Spectra of Rb II, Sr III,YIV, Zrv, Nb vI, and Mo VII in the Vacuum Ultraviolet," J. Opt.Soc. Am. 62, 273-284 (1972).

8J. Reader and G. L. Epstein, "Analysis of the Spectrum of Qua-druply Ionized Yttrium (Yv)," J. Opt. Soc. Am. 62, 619-622(1972).

9 R. Zalubas, J. Reader, and C. H. Corliss, "4s 2 4p4-4s 4p 5 transitionsin five-times ionized yttrium (YVI)," J. Opt. Soc. Am. 66, 35-36(1976).

'0 B. Edl6n, "WellenlAngen und Termsysteme zu den Atomspektrender Elemente Lithium, Beryllium, Bor, Kohlenstoff, Stickstoff undSauerstoff," Nova Acta Regiae Soc. Sci. Ups. (IV) 9, No. 6(1934).

'B. Edlen, "Wavelength Measurements in the Vacuum Ultraviolet,"Rep. Prog. Phys. 26, 181-212 (1963).

12R. L. Kelly and L. J. Palumbo, "Atomic and Ionic Emission LinesBelow 2000 Angstroms-Hydrogen Through Krypton," Naval Re-search Laboratory Report 7599 (U.S. GPO, Washington, D.C.,1973). .

13V. Kaufman and B. Edlen, "Reference Wavelengths from AtomicSpectra in the Range 15 A to 25000 A," J. Phys. Chem. Ref. Data3, 825-895 (1974).

14 Optimization of the level values was done with the computer pro-gram ELCALC, due to L. Radziemski, Jr.

15A. W. Weiss, private communication, 1977.16 E. Luc-Koenig, "Doublet inversions in alkali-metal spectra: Rel-

ativistic and correlation effects," Phys. Rev. A 13, 2114-2122(1976).

17K. T. Cheng and Y.-K. Kim, "Energy Levels, Wavelengths, andTransition Probabilities for Cu-like ions," At. Data Nucl. DataTables 22, 547-563 (1978).

"C. Froese, "Numerical Solution of the Hartree-Fock Equations,"Can. J. Phys. 41, 1895-1910 (1963), and C. Froese-Fischer and M.Wilson, "Programs for Atomic Structure Calculations," ArgonneNational Laboratory Report No. 7404 (National Technical Infor-mation Service, Springfield, VA, 22161).

1288 J. Opt. Soc. Am., Vol. 69, No. 9, September 1979 Joseph Reader and Nicolo Acquista 1288