Measured lifetimes of excited states in Cd

.I. Quanr.

Specrrosc.

Radiot.

Transfer.

MEASURED

Vol.

Il.

pp.

197-201.

Pergamon

LIFETIMES

Press

1971. Printed

OF EXCITED

in Great

Britain

STATES IN Cd*

A. R. SCHAEFER University

of Oklahoma,

Physics

Department,

Norman,

Oklahoma

73069

(Received 24 July 1970)

Abstract---The modified Holzberlein invertron used to measure lifetimes in Mg which were reported in an earlier paper has now been utilizedin Cd. Lifetimesof sixteenstatesin neutral Cd and four in Cd+, including those of the inverted doublet utilized in Cd+-He Penninglasers,have been measured.

1. INTRODUCTION ALTHOUGH there have been some measurements of excited state lifetimes in Cd, they are not numerous. Most measurements have been made on the resonance transitions and on the forbidden line 53P,-51Soil 3261. Due to the lack of excited state measurements, and to the recent interest in Penning lasers, we have used a previously described method”’ to make lifetime measurements in Cd. References to earlier work in Cd were obtained largely from the National Bureau of Standards bibliography of MILEB and WIESE (2) We shall briefly mention here the works to which we have compared our results. There have been many measurements of the 53P,-51S, i 326 1 forbidden line in Cd. Among them are those of KoENrG and ELLET’~’ and SOLEILLET’~’ using a spatial beam decay technique, KING and STOCKBARGER(~)by absorption, WEBB MATLAND, GENEUX and WANDERSand MESSINGER@) by electro n beam excitation, VENCENZ,(@ and BARRAT and BUTAUX(~)by optical excitation, BIENIEWSKI(“) by absorption, BYRON et al.(“) by optical excitation, and MoIsE(‘~’ by absorption. GARSTANG(‘~) has calculated the transition probability for this state. Other measurements include 6’0, + 5 ‘P, 14663 by GENEUX and WANDERS-VINCENZ@) using electron beam excitation, and the transitions 63S1 + 53Po,,,2, A 4678, 2 4800, 2 5086 by LANIEPCE(‘~) using Hanle effect. HELLIWELL(Is) has done a modified self-consistent field

calculation

for this transition.

The principal works which we have used in tabulating reference lifetimes are those of VEROLAINENand OSHEROVICH(‘@ using electron beam excitation with delayed coincidence calculation, a coulomb approximation analysis, WARNER: “) a scaled Thomas-Fermi calculation we did using the method of BATESand DAMGAARD(‘~) and the matrix elements given in GRIEM,(19) the emission study of CORLIS~and BOZMAN,‘~” and the earlier emission measurements of VAN HENGSTUMand SMIT.(“) Of these the measurements of VEROLAINEN and OSHEROVICH,(’6, since they use a modern delayed coincidence technique of measurement,

* Portion

of a dissertation

submitted

in partial

fulfillment 197

of the Ph.D. degree at the University

of Oklahoma.

A. R.

19x

SCHAEFER

for an unspecified portion of their should probably be the more precise. However. results, they used interference filters, which can easily have passed enough fast decaying radiations to have caused the discrepancies with our work. The work of VAN HENGSTIJM and SMIT"') suffers the difficulties of arc intensity measurements. besides being only relative measurements, depending on an absolute value assignment to 326 1 A of 2.1 klsec for their absolute calibration. The work of CORLISS and BWMAN”@ as noted earlier”’ is not entirely suitable for lifetime comparisons.

2.

EXPERIMENTAL

METHOD

The technique used for measurements was the modified invertron source and delayed coincidence data analysis method reported in an earlier paper. “‘A more detailed description and additional references on the method are given there.

-3 R E S LI I>T S

In Table 1 we present the results of our lifetime measurements plus or minus standard deviation of the measurements, which we estimate as the approximate accuracy. compared with the works of others. In Table 2 we give individual lifetime determinations of other authors also for sake of comparison. Table 3 shows lifetime results obtained in Cd’ ion.

4678.4800. 5086 3081, 3133. 3253 3611. 3613. 3466. 3615,3468, 3404 2981. 2981, 2881. 2982,288 I. 2837 5155 4308 3983 6438 4663 4141 3905 326 I ______

6’s~ S"P 7”s

5AP

1X.5*2.0 29.Y-$-4.5

17.6 41 5

5.3D 5’p

147+22 _

x.5

6”D 5’P

18.7+2.4

17.1

7’S xls 9’S_ 5’D 6’0 7’0

5’P 5’1’ 5’P 5’P 5’P 5’P X’D 5’P 5”P,~ 5’&,

I I5i IO 230*2 32718 27.6 f I ..I X5.2& I.2 84.2k4.5 94.1+ 6.8 2490 i 130

7x.7 158.0 791.0 13.3 36.6 78.1 145.0

IO.6 i 0 X

145*

0 X6 24 I

I5

0.57 12*

i 1 1.3*

II

Ih

21* 20.7ri_o.5

44.0 + 2 I)

‘Lo*

6X.5

1360

-3.7

I Y.X5 I .x 37.5 k2.0 65.5k4.5

41*

3300

3100

* Denotes the Coulomb approximation was used to obtain branching ratios for calculation of hfetimeh. Columns { I) and (2) identify the transitions, column (3) gives results of our measurements, column 14) is lifetime? from coulomb approximation. column [5) lifetimes from VEKOLAINENand OSHEROVKH,“~) column (6) lifetimes from WARNER.“‘) column 171 lifetimes calculated from C~RLISS and Borsch.““’ and column j81 lifetime\ calculated from VAN HENGSPUM and SMIT.“”

Measured

lifetimes of excited states in Cd

199

TABLE 2. INDIVIDUAL Cd LIFETIMERESULTSOF OTHERS

44 3261

--

Reference

7 nsec

KOENIG and ELLETT@) SOLEILLET@) KIN<; and STOCKBARGER’~) WEBB and MF_QENGER(@ MATLAND”’ GENEUX and WANDERS-VINCENT’~’ BARRAT and BUTAUX(~) BIENIEWSKI(“‘) BYRON,MCDERMOTT and NOVICK(’ ‘) MOISE”‘) CARSTAN@‘)

2500*250 2450 2100 2140+60 2050 f 50 2180_+70 2250 2500 2390+40 2320 2300

4663

GENEUX and WANDERS-VINCENZ”’

5086 4800 4678

HELLIWELL”~’

7.4

LANIEPCE”~)

9.20 k 0.03

4. DISCUSSION-NEUTRAL

210+20

Cd

(1) 53P, Term The transition at 3261 w of 5s5p3P, -+ 5s2 ‘PO was observed to be a relatively strong transition. There also appeared to be resonance trapping of this line to a large extent, so the following method was utilized to make the measurement. The sample-containing crucible was withdrawn below the cathode to a relatively cool area so that the Cd vapor pressure was quite low (N 10-j pHg). At this pressure there are insufficient Cd atoms present to accomplish electron wave penetration and excitation in the invertron, so a background of H, gas was used. With this gas present the 3261 Cd line was faintly present and could be measured. By using different pressures of H, background and extrapolating to zero pressure Hz, the value of 2.49 + 0.13 psec was obtained. This is lower than the values of CORLISS and BozMAN,‘~‘) and greater than that of VAN HENGSTUM and SMIT,(‘~) who set their reference value equal to that of KING and STOCKBARGER”) of 2.10psec. It is interesting to note the earlier measurements shown in Table 2 tend to agree with ours, TABLE 3. LIFETIMESOF Cd + EXCITEDSTATES

Wavelength (A) iI)

Transition

4416 4136 2749 3251 3536

5s’ *D 512 -+ 7dZ D,,, + 6s’ S 112 + 5s’ ‘0 312 + 5s” =D 312 -+

Note. Columns {l} and results of this work, column

calculation,

and column

{ 2) 5P2P,,, 6p=P,,, 5PZP,,Z 5PZP,,* 5PZP3,2

7 nsec

5 nsec

7 nsec

131

{4)

(51

994 f 54 11.7kO.5 5.7 + 0.9 310+10 290& 10

830+70 4.90 2.89 465+20 465 f 20

(2) identify the transition, column {3} gives (4) lifetimes from a coulomb approximation {5) lifetimes from GENEUX and WANDERS-~INCENZ.“‘)

./\.

‘00

K.

SwAEFm

the intermediate ones tend to be less, and the later ones approach our value again. although remaining a little less. Our measurement of this state is probably not quite so reliable as those of higher excited states. (2) “S Transitions

Each line of the 6”s and 7”s states was measured. Our values for both states do ncjl differ too greatly from the coulomb approximation calculation. Our 6.‘.‘$ value appear somewhat longer than other measurements would indicate. As found with the lowest “S state in Mg, (” there appears to be a heavy cascade. probably 6”P --+ 6’s. of about 85 INC. which makes the analysis of this state admittedly more uncertain than usual. The emission measurements of VAN HENGSITJM and SMIT’“’ and COKLISS and Bo%MAN’~“’ appear to hc clearly too short for both 6”s and 7’.Y. and agreement between ourselves and WAKNIS”-’ is closer for 7-‘S. (3) “D Trtrmitions

In the 5’D multiplet the three lines 361 I- 1% I5, 3466-68, and 3404 were each measured. and similarly in 6”D 298 l-8 t-82 and 288 l-81 were measured. without noticing appreciable fine structure dependence in the multiplet lifetime. This time agreement is excellent fat S3D with VEKOLAINEN and OSHEROVICH,~“’ although except for h-‘D of COKLISS anti BOWMAN.““’ the emission values again appear too short. (4) ’ S Trmsit ior’s Our values for ‘S transitions are markedly longer than those of VIKOLAINEN and OSHEROVICH.“~’ Analysis conditions for this series were quite good (low background. low cascade). Also the coulomb approximation and theory of WARNEK(‘~) predict longcl lifetimes, as does our own experience with the Mg ‘S series. ‘I) Hence we conclude perhap\ the Russian measurements are somewhat in error for this series. (5) ’ D Trumitions

on the ‘D series are in closer agreement with those of VEROLAINEN and for 6’0. It would be of interest to measure higher transitions in this series to investigate a possible anomalous behavior similar to that ofthe ‘D series in Mg. Our results

OSHEROVICH,(“) except

5. DISCUSSION

Cd’

ION

The lifetimes measured in Cd’ are presented in Table 3. There appears to be little other data on Cd’. Of recent interest is the inverted doublet arising from the two electron transition 4d” 5s’ 2D,,2,3,2 + 4d”5p 2f3,2 ,i2, which has been utilized with He to form a Penning laser at wavelengths 4416 8, and 32.51 A. We measured lifetimes of all three possible transitions, obtaining 300 nsec for the life of zD3,2 and 994 nsec for the life of 2Ds,2. Although the values are somewhat different, this same difference in lives of ‘D3,_ and ‘Dsi2 was observed by GENEUX and WANDERSVINCENZ.(22’ These transitions appeared fairly intense, in accordance with the fact that a fairly high cross section for excitation of the 2D upper level, coupled with better than a 100 to 1 lifetime ratio of this state to the lower 52P state can produce the laser phenomena.

Measured lifetimes of excited states in Cd

201

Acknowledgement-The author would like to reacknowledge the assistance of those mentioned in our earlier paper on Mg, and especially the very helpful discussions and consultations with Professor RICHARDG. FOWLER. This work was supported by a NSF traineeship administered by the Graduate College of the University of Oklahoma.

REFERENCES 1. A. R. SCHAEFER, Astrophys. J. 163, I (1971). 2. B. M. MILESand W. L. WIESE,Bibliography on Atomic Transition Probabilities, N.B.S. Special Publication 320 (Washington, 1970). 3. H. D. KOENIGand A. ELLETT,Phys. Rev. 39,576 (1932). 4. P. SOLEILLET, C. hebd. Seunc. Acad. Sci., Paris 196, 1991 (1933). 5. R. B. KING and D. C. STOCKBARGER, Astrophys J. 91,488 (1940). 6. H. W. WEBBand H. A. MESSENGER, Phys. Rev. 66,77 (1944). 7. C. G. MATLAND,Phys. Reo. 91,436 (1953). 8. E. GENEUXand B. WANDERS-VINCENZ, Helv. Phys. Actu 33, 185 (1960). 9. J. P. BARRATand J. BU~AUX.C. hebd. Seanc. Acad. Sci., Paris 253,2668 (1961). 10. T. M. BIENIEWSK~ in Atomic Collision Processes, Proceedings, Ed. M. R. C. MCDOWELL,pp. 1055%1064. John Wiley, New York (1964). 11. 3. R. BYRON,M. N. MCDERMOTT and R. NOVICK,Phys. Rev. 134, A615 (1964). 12. N. L. M~ISE,Astrophys. J. 144, 763 (1966). 13. R. H. GARSTANG,Astrophys. J. 148,579 (1967). 14. B. LANIEPCE,J. Phys. 29, 427 (1968). 15. T. M. HELLIWELL,Phys. Rev. 135, A325 (1964). 16. YA. F. VEROLAINEN and A. L. OSHEROVICH, Optics Spectrosc. 20,517 (1966). 17. B. WARNER.Mon. Not. R. Astr. Sot. 140. 53 (1968). 18. D. R. BATESand A. DAMGAARD, Phil. Tks.‘R. S&. Lond. 242, 101 (1949). 19. H. R. GRIEM,Plasma Spectroscopy, pp. 356361. McGraw-Hill, New York (1964). 20. C. H. CORLISS and W. R. BOZMAN,N.B.S. Monograph 53, U.S. Government Printing Office, Washington, D.C. (1962). 21. J. P. A. VAN HENGSTUM and J. A. SMIT,Physica 22,86 (1956). 22. E. GENEUXand B. WANDERS-VINCENZ, Phys. Rev. Lett. 3,422 (1959).