JOURNAL OF THE OPTICAL SOCIETY OF AMERICA

Absorption spectra of Zni and Cdi in the 1300-1750 A region

Charles M. Brown and S. G. Tilford

E. 0. Hulburt Centerfor Space Research, U. S. Naval Research Laboratory, Washington, D. C. 20375

Marshall L. Ginter*

Institute for Molecular Physics, University of Maryland, College Park, Maryland 20742(Received 2 June 1975)

The high-dispersion absorption spectra of Znz and Cdi have been photographed in the - 1300-1750 Aregion. Observations include the. principal-series transitions ms 2S-msnp lP', the electric-quadrupoletransitions mSs IS-msnd 'D2, and the intercombination transitions MS2 IS-msnp 3X' (m=4 and 5 forzinc and cadmium, respectively). Energy levels are presented for msnp

1 p (m < n c 66), insnp 'L2

(mi 4 < n • 20 for Zni and m = 5 < n • 26 for Cdi) and msnp3P' (in 4 < n < 12 for Zn i andin = 5 < n <31 for Cdi). The ionization potentials of Zni and Cdi determined from the msnpIPo seriesare 75769.33 t 0.18 cm-' and 72540.07 - 0.18 cm-', respectively. At high metal-vapor pressures in thepresence of argon, diffuse satellite lines appeared with the strong atomic transitions.

Index Headings: Absorption; Spectra; Zinc; Cadmium; Ultraviolet.

The spectra of Znr and Cdi have been studied exten-sively in the regions of wavelengths longer than-2000 A1-6 and between -600 and 1300 A. 7-9 Noticeablyabsent are high-resolution data for the - 1300-2000 Aregion. The present work on the absorption spectra ofZni and Cdi is directed toward filling this gap in theexperimental observations.

The - 1300-2000 A region of the spectra of Zni andCdi is particularly important because it contains mostof the possible transitions between the ground state(ms2 IS0, m = 4 and 5 for zinc and cadmium, respec-tively) and excited energy levels converging on theground state (Ms 2S1/2) of Znix or Cdii. Here we re-port the results of our studies of the dipole-allowedMs2 1So-msnp1P' principal series, the intercombinationms2 'So-msnp 3P', transitions, and the electric quadrupoletransitions ms2 'So-msnd 'D2 in Zni and Cdi in the 1300-1750 A region. We have observed many relatively weakspectral lines and extended the msnp 1Po, 3Po andmsndlD2 series to high values of the quantum number n.

EXPERIMENTAL PROCEDURES

The apparatus and procedures have been discussedin detail in a previous paper' 0 and in connection withsimilar studies on Cai, 11 Br, 12 and Sir.13 Briefly,zinc'4 or cadmium14 was placed in a King-furnace sys-teml' equipped with a stainless-steel liner tube. Theliner tube (- 150 cm long) was heated to temperaturesin the range 250-6000C, with the temperature monitoredby a Chromel-Alumel thermocouple. Absorption spec-tra of the resulting zinc or cadmium vapors were photo-graphed in the third and fourth order of a 6. 6 m vacuumspectrograph (reciprocal dispersion -0.4 and 0. 3 A/mm,respectively). Exposure times were approximately30 min on Kodak SWR emulsions. Microwave-excitedrare-gas lamps"5 were used to provide backgroundcontinua. Exposures were obtained at pressures rangingfrom 10-4 to 200 torr, although most experiments wereperformed with a furnace atmosphere of argon at pres-sures of - 10-15 torr. Iron-arc lines from the secondorder of the grating were used as a comparison spectrum,and absorption lines from several well-known carbon

monoxide bands1 8 (which are due to an impurity in thefurnace atmosphere) insured the elimination of wave-length shifts between different exposures. Plate mea-surement and data reduction were performed as de-scribed previously. 10 The uncertainty of absolute wave-length is estimated to be within A± 0. 003 A (equal to-0.18 cm' at 1320 A and -0.10 cm' at 1750 A). Theuncertainty of the relative position of sharp, unblendedlines is somewhat smaller, and the uncertainties asso-ciated with broad, blended, or diffuse features are con-siderably larger.

RESULTS AND DISCUSSION

The wavelengths and wave numbers of the lines ob-served for the transitions 1s22s22pP3s23pP3d'04s2 150 to4snp'P" (n = 4-66), 4snd'D2 '(n=4-20), and 4snp3 P'(n = 4-12) in Zni are listed in Tables I, II, and m,respectively. Analogous data for the ... 5s2 'So-5snplPc (n= 5-66), 5snd'D12 (n= 5-26), 5snp3P'(n = 5-31) transitions of Cdi appear in Tables IV-VI.The line assignments that appear in Tables I-VI willbe discussed briefly in the following sections.

A. S2 IS-np t'P transitions

Transitions from the 'S ground state to members ofthe np1P' series are dipole allowed by L-S selectionrules, and are the strongest series observed in absorp-tion in the -1300-1750 A region of both Zni (see Figs.1 and 2) and Cdi. BasedontherelationTn=T..-R(n-Y)- 2

and the assumption that the quantum defect 6 becomesconstant at large n (see Fig. 3), we obtain ionizationlimits of 75 769. 33 cmn, for Zni and 72 540. 07 cm-' for

1319.8 A 1339.9A

20 112 np1P,116 112 nd'D2

'IG. 1. High-n members of the Zn I absorption series. TheCd r absorption spectrum is similar in appearance.

1404

VOLUME 65, NUMBER 12 DECEMBER 1975

ABSORPTION SPECTRA OF Zn I AND Cd I

(n -1) dD nd3 F'l .I

TABLELIZn i.

Observed lines of the 4s2 1S0-np 4P' transitions in

n=7

k\ '1/

n = 8

n = 9

i 450 C

6000C

450"CI A1

600° C

450 C

6000C

*A AFIG. 2. Low-n members of the Zn i absorption series. -Thetriangles mark the positions of satellite lines (see Fig. 4 andtext).

Cdi. The absolute errors in these values are -± 0. 18 cmn<and the relative errors t0 are -± 0. 04 cm71. The Ryd-berg constants were taken as 109 736. 40 cm1 and109 736. 78 Umn' for zinc and cadmium, respectively.

The wavelengths in Tables I-VI were measured fromplates obtained at the lowest pressures of argon andmetal vapor that produced measurable spectral lines.In zinc, several diffuse satellite lines are observedtoward the red of the strongest 4s2 1S-4snp 1P0 tran-sitions whenever the zinc pressure is high and argonis present. Figure 2 illustrates these effects for sev-eral low n-value members of the zinc spectrum. Figure4 illustrates the variation of the separation of the diffusesatellite lines from the main 'S-VP' lines as a functionof the principal quantum number. In addition, at thehighest pressures a single satellite line was observed-30 cm-t to the violet of the 4s 2 'S-4s6p PY transition.Satellite lines were observed near the 5s2 'S-5s6p 'P'cadmium line. Additional satellite lines were not ob-served in cadmium because the spectrum was photo-

2.00-.2 1.00

1A snplP,°

(np) (nd)

2.20- -. 20

Asnp P, \*snd'D2

2. 1.40

n 10 20 22 40 f

FIG. 3. Quantum-defect plots for the 4snp 1 '3P3 and 4snd 1 D2levels of Zn I. The quantum-defect plots for the correspondinglevels of Cd i are similar.

n (va) v (cuum) ( r*n (vacuum) (vacuum) (upper term)

V Al V

-456789

101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566co

2139.2471589.5671457.5701404.1191376.9111361.1111351.0981344.3431339.5691336.0671333.4221331.3751329.7581328.4571327.3951326. 5191325.7851325.1661324.6391324.1841323.7921323.4491323.1491322.8841322.6501322.4421322.2551322.0881321.9371321.8001321.6761321.5631321.4611321.3671321.2801321. 2001321.1281321.0601320.9971320.9391320.8841320.8351320.7881320.7441320.7031320.6651320.6291320.5951320. 5631320.5331320.5051320.4781320.4541320.4301320.4071320.3861320.3671320.3461320.3271320.3101320.2931320.2791320.2651319.795

46745.4, a62 910.268 607. 3671 219.0672 626.3273469.3774013.8774385.8074 650.8774 846.5474994.9975 110.3175201.6775275.3175 335.5075 385.2575427.0075 462.2775492.2875 518.2175 540. 5975 560.1775577.2775 592.4275 605.8175 617.6775 628.4075637.9275 646.5975 654.4175 661. 5075 667.9575 673.8475679.2275 684.1975 688,7675692.9075 696.7975 700.4075 703.7375706.8575709.6875 712.3675714.8875 717.2575719.4575 721, 5275 723.4375725.2775726.9975728.5875 730.1575731.5375732.9175734.2475 735.4475736.5475737.7175738.8475739.8075740.7975741.5875742.3875 769.33

aTaken from Ref. 3. Wavelength calculated from this value.

nd 1PII

Defc. 1975 1405

1. 94452.92133. 91434. 91095. 90886. 90747. 90648. 90609.9052

10. 905011.904512. 904113. 903714. 904015. 904316. 903017.904118.904419.902020.904321. 903022.905323. 903224.905725. 905426. 899227.904528.897629.900830.901431. 901132. 90033. 90034. 89735. 90136. 90537. 89238. 89439. 90040. 90041. 90942. 89143. 88944.89345. 90346. 90447.90948. 89649. 90650. 91051.8952.9253.8854.8955.9256.9057.958.960.061.062.062.963.8

BROWN, TILFORD, AND GINTER

TABLE IT. Observed lines of the 4s2 1S,-nd 1D2 transitions ofZn I.

X (A) v (cmn1

)

n (vacuum) (vacuum) (upper term)

4 1601. 063 62458.50 2.87135 1 4 6 3 . 3 0 4 a 68338.5 3.84296 1407.438 71051.11 4.82277 1378.987 72 516.98 5.80878 1362.483 73 395.42 6.79909 1352.048 73 961.89 7.7919

10 1 3 4 5 .0 2 3 b 74348.18 8.787311 1340.074 74622.77 9.783112 1336.451 74 825.05 10.780213 1333.721 74 978.20 11.777514 1331.610 75097.09 12.776515 1329.945 75 191.06 13.775616 1328.610 75 266. 61 14.774517 1327.520 75 328.42 15.776118 1326.624 75 379.33 16.774219 1325.873b 75422.01 17.775020 1 3 2 5 .2 3 8b 75458.13 18.7783

aBlended with an emission line.bBlended with a CO line.

graphed with lower pressures of metal vapors than zinc.Ch'en and Wilson17 and Jefimenko and Williams 18 ob-served similar satellite lines in spectra of the alkalimetals and have attributed the observed effects to tran-sitions in the quasimolecular systems formed duringcollisions of metal atoms with foreign gases.

B. s2 "S-nd ID2 and np 3P: transitions

Transitions from the 1S ground state to members ofthe nd 'D2 series have been observed in both Zni (seeTable IB) and Cdi (see Table V). These transitionsoccur between states of the same parity and with A J= 2;hence, they obey the selection rules for electric quadru-pole transitions. 19 Similar electric-quadrupole tran-sitions have been observed in the absorption spectrumof argon, 20 magnesium, 21,22 and calcium. 2' The5577 A (lD2 -'S) auroral line of OI is a well-known ex-ample from emission spectra. The 'S--nd D2 transi-tions are weak in both Znr (see Fig. 2) and Cdi, andare observable only when the vapor pressure of the metalis high.

TABLE m. Observed linesZn a.

of the 4s 2 'So-n 3PI transitions in

X (A) v (cmur) n*a (vacuum) (vacuum) (upper term)

4 3076.789 3 2 50 1.4 2a 1.59255 1632.002 61274.45 2.75156 1468.846 68080.65 3.77797 1408.803 70982.23 4.78788 1379. 329 72499.00 5.79279 1362.526 73 393.07 6.7956

10 1352.003 73964.33 7.797211 1344.956 74 351.85 8.798712 1340.001 74 626.80 9.8003

'Taken from Ref. 3. Wavelength calculated from this value.

TABLE IV. Observed lines of the 5s2 is-ome 1Pj transitions inCd I.

n (a) v (cmuum) (en (vacuum) (vacuum) (upper term)

56789

10111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656600

2288.7281669.2461526.6851469.3051440.1101423.1361412.3651405.0921399.9461396. 1 6 8b1393.3121391.1011389.3531387.9461386.7971385.8481385.0531384.3821383.8101383.3181382.8921382.5201382.1961381.9081381.6531381.4281381.2251381.0431380.8801380.7311380.5961380.4741380.3621380.2601380.1661380.0791379.9991379.9261379.8581379.7941379.7351379.6811379.6311379.5821379.5381379.4961379.4571379.4201379.3861379.3521379.3221379.2941379.2661379.2401379.2161379.1921379.1701379.1491379.1291379.1101379.0931379.0761378.548

'Taken from Ref. 6.bBlended with a CO line.

43 692. 38"59 907.2865 501.41a68 0 5 9 . 3 9 a69439.1370267.3770 803.2571 169.7371431.3571624.6171771.4371885.5371975.9772 048.9272 108.6272157.9872199.3972 234.4172264.2672 289.9672 312.2172 331.6772 348.6572 363.7172377.0572 388.8872 399.5272 409.0372417.6172425.4272432.4772438.8972444.7672450.1472455.0772459.6272463.8272467.6572471.2472474.5972477.6672480.5072483.1772485.7072488.0572490.2472 492.3172494.2272 496.0272497.8072499.4172 500.8872 502.3172 503.6872 504.9872 506.2472 507.3872 508.4972 509.5472 510.5372 511.4572 512.3372540.07

1.95042.94733.94854.94885. 94886.94877.94878.94879.9487

10.948511.948512.948213.947614.947515.948216.947017.947518.947719.946720.946521.945322.947123.943224.944625.945126.941127.942228.938429.93530.93831.93532.93333.93234.93235.93136.93337.93638.92739.92940.93841.93242.92043.91644.92645.92946.92847.93448.9249.9150.9551.9552.9253.9154.9155.957.057.958.960.060.961.962.9

Wavelength calculated from this value.

Vol. 651406

ABSORPTION SPECTRA OF Zn I AND Cd I

TABLE V. Observed lines of the 5s2 1S0-nd 1D2 transitions inCd I.

A (A P (m t)n*n (vacuum) (vacuum) (upper term)

5 1688.626 59 2 19. 73a 2.87026 1535.278 6 5 1 3 4 .7 8 a 3.84957 1474.091 6 7 8 3 8 .4 0 aB 4.83118 1443.064 69 296.99 5.81709 1425.120b 70169.52 6.8038

10 1413.712 70735.75 7.798611 1406.059 71 120.77 8.793012 1400.664 71394.72 9.788313 1396.718 71 596.41 10.783714 1393.739 71749.45 11.781315 1391.437 71 868.14 12.779516 1389.624 71 961.89 13.776717 1388.167 72037.46 14.776118 1386.979 72 099.12 15.775419 1385.999 72150.15 16.776020 1385.182 72 192.69 17.773521 1384,490 72228.77 18.775322 1383.905 72 259,31 19.770124 1382.961 72308.62 21.774525 1382.581 72328.51 22.775026 1382.247 72345.95 23.7761

aTaken from Ref. 6. Wavelength calculated from this value.bBlended with a CO line.

The s21S-snp 3P' series observed in Zni and Cdi(see Tables III and VI) are dipole forbidden for pureL-S coupling, but are allowed when the 3 P' level has a

-300-

A

( cmlT)

-200"-1

-100-

5I I

1 0 n 1 5

FIG. 4. Plot of A, the separation from the 4s 21 S0 -4snp 1Ptransition, for the satellite lines observed in Zn i. A is nega-tive, because all satellite lines shown are at lower frequencythan the corresponding principal series line. A single satelliteline was observed -30 cm- above the 1So-6p 1 P' transition underthe conditions of highest temperature and pressure.

TABLECd I.

VI. Observed lines of the 5s2 IS,-np 3P, transitions in

A (A) v (cmn1 ) n*n (vacuum) (vacuum) (upper term)

5 3261.995 30 656. 09a 1.61866 1710.518 58 461.83 2.79197 1537.830 65 026.71 3.82178 1474.012 6 7 8 4 2.0 6a 4.83309 1442.567 69 320.89 5.8385

10 1424.589 70195.70 6.841711 1413.300 70756.39 7.843612 1405.730 71137.42 8.845113 1400.402 71408.07 9.845814 1396.512 71606. 98b 10.844615 1393.569 71758.22 11.847216 1391.300 71875.22 12.847417 1389.509 71967.85 13.848218 1388.073 72 042.31 14.847919 1386.901 72 103.22 15.849320 1385.931 72 153.65 16.851821 1385.119 72 195.94 17.857322 1384.435 72 231.63 18.862123 1383.852 72 262. 05 19.867324 1383.355 72 288.04 20.866525 1382.921 72310.70 21.873026 1382. 545 72330.36 22.875327 1382.220 72 347. 39c 23.864828 1381.929 72362.61¢ 24.867129 1381.671 72 376.120 25.871430 1381.445 72387.970 26.860331 1381.239 72398.760 27.8670

'Taken from Ref. 6. Wavelength calculated from this value.bBlended with a CO line.'Shoulder measurement.

small amount of 'Po character. The occurrences ofthese transitions indicate that there is a slight depar-ture from pure L-S coupling in both atomic species.For zinc the observed 1S-4snp3P' transitions are lessintense than the 'S-4snd 1D2 electric-quadrupole tran-sitions (see Fig. 2), indicating that the terms from the4snp and 4snd configurations are predominantly L-Scoupled for n values in the range that corresponds toour observations. For cadmium the IS-5snp 3 P' tran-sitions are more intense than the 1S- 5snd 'D2 transi-tions, especially at higher n values, which indicatesa slightly greater departure from L-S coupling fromZni to Cdi. Garstang23 has reported transition prob-abilities for the first members of the ISo- 3P and'S 0-'Po series for the Mgi, Zni, Cdi and Hgi sequence.The ratios of the 'SO_3Po to the 'S0-1 P' transition prob-abilities for this sequence are 6. 8x 10-7, 6. 9x 10-,7. 6 x 10-4, 1. 3 x 10-2, indicating that the 'P, contri-bution to the 3 P, wavefunction is 0. 003%, 0. 02%, 0. 2%,3. 2%. 24 We observe the strength of the electric quadru-pole transitions to fall midway between the strengthsof the intercombination lines of Zni and Cdi, or about2 x 104 times the strength of the 'So-1 P' transitions.Using Garstang' s value for the ISo-lP1 transition prob-abilities 5. 2 x 108 sl for Zni and 5. 6 x 108 sr' for Cdrwe estimate a transition probability of 1 X 105 S7l for

the 1So-1D2 transitions.

1407Dec. 1975

0 0-* N../ \ --.. ..-0*--*-*

BROWN, TILFORD, AND GINTERVo

TABLE VII. Energy levels (in cmt) for Zni.

Designation J Level Interval Designation J Level Interval

4s2 S

4p sPI

4p 1p.

5s 3S

5s Is

5P 3P.

4d 1D

4d 3D

5p lpO

6s 3S

6s1 S

6p 3Po

5d 1D

5d3D

6p tpI

4f 3F'

4f iF7s 3s

'7s Is

7P 3PI

6d 1D

6d 3D

7P PI

5f IF

8s 3 S

8s1S

8p 3po

3

1

0

012

0.00

32311.3332 501.4132 890.34

46 745.40

53 672.26

55789.22

61 247.9061274.4261330.89

62 458.52

62768.7662772.0262776.99

62 910.43

65 432.33

66 037.68

68 070.8668 080.6768 101.79

68 338.49

68 579.1668 580.7068 583.10

68607.27

68833.7968833.9368834.03

68 835.00

69745.96

70 003.72

70 977.170 982.2370 992.2

71051.11

71212.1671213.0071214.27

71219.05

71336.15

71822.7

71956.2

72496.672 499.0072 504.2

190.08388.93

26.5256.47

3.264.97

9.7121.12

1.542.40

0.140.10

5.110.0

0.841.27

2.45.2

7d'D

8p iPI

7d3D

9s 3S

9s Is

9p 3 p0

2

1

1,2,3

1

0

012

2

1,2,3

1

1

1

2

1

1,2,3

1

1

2

1,2,3

1

1

2

1

1

1,2,3

2

1

1,2,3

2

1

1,2,3

2

1

1,2,3

2

1

8dlD

8d 3D

gp ipO

los 3S

1op 3p°

9d 1 D

9d3D

l1s 3S

11p 3P°

.10d'D

10d3D

llp tP°

12s 3S

12p 3 P

12p 'P°

1ld3D

12d ID

13p 'P°

12d 3D

13d1 D

14p 1P'

13d 3D

14dt D

15p P°

14d 3D

nd iD

lp Spi

72 516.98

72 626.32

72627.9

72 983.2

73 060.6

73 390.773 393.0773 395.9

73 395.42

73 470.

73 469.37

73 698.8

73 964.33

73 961.89

74 013.87

74 016.

74169.0

74 351.85

74 348.18

74 387.6

74 385.80

74495.8

74 622.77

74 626.80

74 650.87

74 651.3

74 825.05

74846.54

74 855.1

74 978.20

74 994.99

74 994.0

75 097.09

75 110.31

75112.2

n=15-20'

n= 1 6 - 6 6 b

2.42.8

bSee Table I.'See Table rI.

C. Discussion

The n* values listed in Tables I-VI were computedby use of the series limits listed in Sec. A. Thesedata can be used to construct plots such as Fig. 3,

which indicate (a) that the quantum defects of all sixof the observed level series follow regular coursesand (b) that the apparent series limits for the np 'PO,3P, and nd 1D2 series of each atom are identical. Hence,there is no indication that these series are strongly

1408 Vol. 65

ABSORPTION SPECTRA OF Zn i AND Cd i

perturbed by interloper levels, as was suggested pre-viously. 5 The 7d1D2 level- reported previously" 3' 6 forZn, is erroneous. The interaction, if any, of the ndlDlevels with the 4pj91D level is probably strongest atlow n. 4,25

Earlier work on the energy levels of Zn, that existbelow the 4s 2S,1 2 limit of Znii have been summarizedby Moore' and by Johansson and Contreras. 3 The morerecent listing3 was based partly on new measurementsand partly on data previously published by Hetzler,Boreman, and Burns. 2 A careful review of existingdata indicates that the energy-level values listed byJohansson and Contreras are reliable to within a fewhundredths of a cm1 , with the exception of values basedon older measurements termed unreliable by the orig-inal workers. 2 Table VII provides a summary of theenergy levels of Zni observed below the first ionizationlimit, with the number of recorded digits indicatingour order of magnitude estimates of the relative re-liabilities of the various values. Data used in compil-ing Table VII appear in Moore,1 Johansson and Contreras, 3Hetzler et al., 2 and in Tables I-rn. The unpublisheddata of Dick26 on the emission spectrum of zinc werevery useful in confirming the existence of a number ofexcited levels. For energy levels of Zni occurring abovethe first ionization limit, the reader should consultRefs. 4, 7, and 28.

The reader is referred to the data presented inMoore, ' Burns and Adams, 6 Danker, 27 and Tables IV-VIfor a detailed listing of the energy levels of Cdi existingbelow the 5s 2S 1l limit.

ACKNOWLEDGMENTS

The authors wish to thank R. H. Naber for his assis-tance with the experimental portions of this work andDr. K. Dick for providing us with a copy of his un-published data on the zinc emission spectrum.

*Partially supported by the E. 0. Hulburt Center.'C. E. Moore, Atomic Energy Levels, Vol. X, Nail. Bur.

Stand. (U. S.), Circ. No. 467 (U. S. Government Printing

Office, Washington, D. C.), p. 124 (1952); Vol. HI, p. 55(1958).

2 C. W. Hetzler, K. W. Boreman, and K. Burns, Phys. Rev.48, 656 (1935).

3 I. Johansson and R. Contreras, Ark. Fys. 37, 513 (1967).4W. C. Martin and V. Kaufman, J. Opt. Soc. Am. 60, 1096

(1970).5W. R. S. Garton and A. Rajaratnam, Proc. Phys. Soc. A68,

1107 (1955).6K. Burns and K. B. Adams, J. Opt. Soc. Am. 46, 94 (1956).7W. R. S. Garton and J. P. Connerade, Astrophys. J. 155, 667

(1969).8G. V. Marr and J. M. Austin, J. Phys. B 2, 107 (1969).9G. V. Marr and J. M. Austin, Proc. Roy. Soc. A310, 137

(1969)."0C. M. Brown, R. H. Naber, S. G. Tilford, and M. L.

Ginter, Appl. Opt. 12, 1858 (1973)."C. M. Brown, S. G. Tilford, and M. L. Ginter, J. Opt.

Soc. Am. 63, 1454 (1973).12 C. M. Brown, S. G. Tilford, and M. L. Ginter, J. Opt.

Soc. Am. 64, 877 (1974),3C. M. Brown, S. G. Tilford, R. Tousey, and M. L. Ginter,J. Opt. Soc. Am. 64, 1665 (1974).

t 4Atomergic Chemicals Co., 99.9999% purity.1 5P. G. Wilkinson and E. T. Byram, Appl. Opt. 4, 581 (1965)."S. G. Tilfotd and J. D. Simmons, J. Phys. Chem. Ref. Data

1, 147 (1972).17S. Y. Chen and R. A. Wilson, Jr., Physica 27, 297 (1961),

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(1965) and references therein.18R. H. Garstang, in Atomic and Molecular Processes, edited

by D. R. Bates (Academic, New York, 1962), p. 4.20K. Yoshino, J. Opt. Soc. Am. 60, 1220 (1970).2IC. M. Brown, M. L. Ginter, and S. G. Tilford, unpublished

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examination of the quantum defects for the 3pnd 'D2 levels ofMg i for 3:n•13 [G. Risberg, Ark. Fys. 28, 381 (1965)]confirms that six lines classified 352 1 S0 -3snp 3 Pi, 21 < n $ 26,by Codling are the electric quadrupole 3s2 IS0 -3snd 1D2 transi-tions with 20 -n- 25.

23R. H. Garstang, J. Opt. Soc. Am. 52, 845 (1962).24A. Lurio, M. Mandel, and R. Novick, Phys. Rev. 126, 1758

(1962).25W. C. Martin, private communication, 1975.28K. Dick, private communication.27H. Danker, Spectrochim. Acta 19, 1443 (1963).2 8W. H. Parkinson and E. M. Reeves, Proc. Roy. Soc. A331,

1585 (1972).

Dec . 1975 1409