Atomic transition probabilities for Sn(I), Sn(II) and Cl(I) lines in the 5300–6850 Å wavelength range

1. Qualt. Spectrosc. Radiat. Transfer, Vol. 18, pp. 509-514. P ~ n

Press 1977. Printed in Great Britain

ATOMIC TRANSITION PROBABILITIES FOR Sn(I), Sn(II) AND CI(I) LINES IN THE 5300-6850 WAVELENGTH RANGE T. WuJ~? and S. WENIGm Observatoirede Paris, Sectiond'Astrophysiquede Meudon,F. 92190Meudon,France (Received 30 March 1976)

Abstract--Absolutetransition probabilitiesfor fifteenSn(I)lines,nine SnCII)lines and six CI(I)lines have been measured in the spectral range 5400.-6850~ by using a wali-stab~ arc. The elements were introduced to the arc chamber as gas mixtures containing small amounts of SnCI4in argon. Plasma diagnosticwas carriedout by line-intensitymeasurementsand by numericalsolutionof the equationsfor a perfect gas. Measured transition probabilities are comparedwith theoreticalcalculations and other experimental values. Discrepancieshavebeenfoundto be greaterthan the experimentaluncertainties.However,for two Sn(II) lines, agreementis satisfactory. 1. INTRODUCTION IN A PREVIOUSpaper, ~) absolute transition probabilities were given for a number of Sn(I) and Sn(II) lines in the spectral range 2317--4525/I,. One experimental value has been given by C o ~ s s and B o z ~ ~2~for the Sn(I) 5631.71 ~ line for which theoretical values were calculated independently by LAWRENCE°~ and by GRUZDEV.c4~ For Sn(II) 6453.50~ and 6844.05 ~, the calculated A values were given by KUNISZand MmD~K c5~and by MmDAL~K.~6) The aim of this paper is to present additional A values for lines emitted by an arc plasma containing Ar, Sn and Cl, 2. EXPERIMENTAL Absolute transition probabilities were determined from the emission spectra produced in a wall-stabilized arc operating at atmospheric pressure. The arc geometry allows a homogeneous flow of a mixture of tin tetracldoride vapour and argon through the entire length of the discharge channel. The homogeneity of the plasma was checked by side-on observations, t~) Line-intensity measurements were made at different distances from the anode. The observed intensity distribution along the arc axis was nearly horizontal. The resonance lines of Sn(I) do not show self-reversal, thus suggesting that cooler layers do not occur along the arc-plasma column. End-on measurements of the line-intensity were taken close to the axis, where the concentration gradients of plasma components could be neglected. The experimental arrangement is shown in Figs. 1 and 2. Figure 1 shows the longitudinal section of the cascade arc in a horizontal plane. Argon is introduced to the arc through holes at the rate of 1.5 l/min. In this manner, contamination of the observation windows by tetrachloride is avoided. Figure 2 shows a cross section of the arc in a plane perpendicular to the axis. Argon is introduced into the arc chamber at 8 llmin through an orifice. A gaseous mixture of argon and SnCh is created, introduced into the arc channel through a vertical slit and pumped out by an electric fan (not shown in Fig. 1), A thermostatic system, made up of an electric furnace, a thermoelement, a thermoregulator and a cooled vessel maintains the temperature of the liquid SnCh in a range 20-100°C to an accuracy of -+ I°C. Thus, the partial pressure of the vapor introduced may be adjusted precisely. Two series of experiments were needed for each wavelength interval to take account of significant variation of line intensities in the spectrum. For strong spectral lines, the temperature of the vaporizing liquid was TI = 48~C and the arc-current intensity I = 28 amp (Experiment I), whereas for weak lines they were T = 80°C, I = 22 amp (Experiment II). The plasma radiation along the arc axis was photographed with a large-grating spectrograph in an.Ebert mounting. A telecentric system was used and the enlargement was ~'Permanentaddress: Instytut FizykiW.S.P., 45-951Opuleul. Oleska 48, Polska. 509

51'0

T. WuJEc and S. WEmOER

Fig. 1. Longitudinalsection of the cascade arc (in a horizontalplane); 1, electric insulator; 2, water-cooled copper rings; 3, argon inlets; 4, quartz windows.

16 i

16

-------3

m9

Fig. 2. Cross-sectionof the arc (in the plane perpendicularto the axis); 1, tMrmoelement;2, containerwith SnCI~; 3, water inlets; 4, argon inlets; 5, gas outlet; 6, water outlet; 7, cooled vessel; 8, electric heater; 9, SnCL,inlet. found to be 1:1. For each experiment, the two spectral ranges (i.e. 4250-4550/~ and 53006850 J~) were recorded successively. Data for the 4250-4550 J~ range were obtained by using a holographic (3000 lineslmm) plane grating, a Kodak 2 A filter and Kodak II aO plates. The 5300--6850~ range was photographed using Kodak II aF plates, a Bausch and Lomb 288 lines/ram grating and a Kodak 12 A filter. An absolute intensity calibration was carried out by using a carbon arc as primary radiation standard, following EULER0~ the anode consisted of spectrally pure Ringsdorf RWO graphite. 3. PLASMA DIAGNOSTIC AND DATA REDUCTION The plasma diagnostics were based on the assumptions that local thermodynamic equilibrium (LTE) exists and that the plasma is optically thin. Because only a small amount of SnC14 vapour was introduced into the discharge chamber, the plasma can be considered to be composed of argon only. L T E has been verified experimentally in argon plasmas by several authors cs-m for electron densities of about 5 × 10t5 cm -3. The experimental results do not appear to satisfy the validity criteria for complete LTE established by Gltm~/°2> for hydrogen and

Atomic transition probabilitiesfor Sn(I), Sn(II) and CI(I)lines

511

hydrogenic ions. However, recent theoretical calculations (t3) show that LTE is met in an argon plasma at lower electron densities (ne---10 t6 cm -3) for optically-thick resonance lines. The plasma parameters were determined by solving the equations of Clapeyron-Dalton for a quasi-neutral, perfect gas and using the Saha equations for tin, argon and chlorine, and those for line-emission coefficients (one equation is needed for each element). The partition functions for A(I), CI(I) and CI(II) were obtained from the tables of DRAWlNand FELENSOK(14~and those for Sn(I) and Sn(II) were derived from the data of HAL~NKAand GRA~OWSKI.°5) The lowering of the ionization potential, which occurs under our plasma conditions, was determined according to the expressions given by GRUNDF.L.(16'17>Plasma diagnostics were performed with the help of a program elaborated in Ref. (1) and carried out on the Odra 1204 computer. Temperatures and densities were determined from intensity measurements of A(I) 4300.1 A, CI(I) 4226.4 ,~ and Sn(I) 4525.7 ,~. The optical depths for the lines studied were checked by comparison of their peak intensities with blackbody radiation at corresponding temperatures and wavelengths. The observed lines are generally slightly affected by self-absorption; they are easily used for transition-probability determinations. However, some strong lines for which the peak intensity is about 10-25% of the Planck function [e.g. Sn(II) 6453.50 ~ (Experiment II) and Sn(I) 4524.70 .~, 6149.71 ,~, Sn(II) 5561.95 .~, 5588.92 ~, 5799.19 ~ (Experiment I)] were corrected for self-absorption by a method applied to not-quite-optically-thin plasmas with 0<~, <0.5. (~) Numerically, the expression 14 = - B~ In [1 - (IA~IB~)] was applied over the entire line profile. In this equation, I~~ denotes the measured intensity, 14 defines the intensity radiated from optically thin layers, and BA is the Planck function at given A and temperature. This procedure is correct for lines with negligibly small instrumental distortion. The very intense lines, e.g. Sn(II) 6453,50 ~ (Experiment I) were rejected. Line intensities were computed from numerical data derived from recorded line profiles by using a program prepared by Morn'. (tg) The transition probability is obtained from the expression Am - 4~- 1 Am,U(T) 1 exp (EIIkT), hc ! g= N where I, gin, U(T), N, ! and T are, respectively, the line intensity at wavelength A, statistical weight of the upper level m of an atom or ion, partition function, particle density, plasma length, and temperature. Relative A values may be determined from measured ratios of lines. These A values can be converted to an absolute scale if one absolute A value is known. The absolute scale was determined for Sn(I) and CI(I) lines by using A values for A(I) 4300 ~, CI(I) 4226 ]k given by WmsEt2°) and :an A Value for Sn(I) 4525 J~ obtained by WmEC and MOSmLOK.(~) Relative A values for Sn(II) were adjusted to an absolute scale using Saha's equation and appropriate plasma measurements. 4. RESULTS Data obtained for our two experimental series are shown in Table 1. The observed electron densities are in good agreement with data obtained from half-width measurements of A(I) 4300.10 A. They are 1.01 x 10t6 and 1.46 x 10t6 cm -3 at 9235°K and 10,260°K, respectively. Data in Table 1 show differences between the concentrations of the plasma components (Sn and CI) and the stochiometric value corresponding to SnCi, Previous experiments (t) have shown that the deviation from stochiometric composition is greater for higher temperatures (i.e. near to the plasma axis). Here, the densities of Sn and CI are evaluated independently of line-intensity measurements; the plasma parameters are not affected by demixing. According to the criteria of GRIEM(12) and DRAWtN,(2t) LTE can be expected under our experimental conditions for tin atoms as well as for ions, and partial LTE should obtain for argon and chlorine atoms. At equilibrium, determination is possible of the relative transition probabilities for Sn(I), Sn(II) and CI(I) lines when the temperature is known. To check the derived plasma temperature To, the excitation temperature Tex¢ has been evaluated from a Boltzmann plot (indicated (~) by Roman numerical IV) using physical conditions corresponding approximately to those of our two experiments. The transition probabilities given by PENKn~ and S I ~ v ~ m (') have been used. The temperature Text has been found to be 570°K higher than Tp. An approximate temperature difference has

512

T. Wumc and S. WENIGER Table 1 Data derived from plasma diagnostics. I

:

:

: :

: :

:Temperature(°K)

:

9235

+

35

:

10269

+

42

:

0.733

x

1016

:

1.378

x

IO 16

0.759

x

1018

:

0.685

x

1018

Ne

:

EXPERIMENTAL SET I ; T f = 8 0 ° C ~ I = 22 amp.

: :

EXPERIMENTAL SET I I ; T f = 4 8 " C ~ I = 28 amp.

;NAI z

::

0.345

x

IO 16

:

O.128

x

IO 17

•:NcII-

:

0.208

x

IO 17

:

0.455

x

1016

:NcIII

:

O,IO2

x

10 16

:

0.726

x

IO 15

:Nsn I

:

0.577

x

IO 14

:

2.702

x

IO 12

:.NSnII

: :

0.286

x

IO 16

:

2.250

x

IO 14

:.N S n I I I

:

0.408

x

IO 13

:

1.223

x

1012

The number d e n s i t i e s

are given

i n em

[

-3

Table 2. Transition probabilities for Sn(I) lines in the spectral range 5630--6354/~. ::

::

.

::

: ~=~

:

:

;sp 2 ,8 ° - 6.3p?

=

:

5631.71

THIS W O R K

2.37

:

÷

5753.59

: :

0.780

~

0.35

:

:

0.484

~

0.20

:

:

:6.3p; 7p' o

::

5761.76

:683p;

:

5925.44

:

2.20

÷

0.95

5970.30

:

9.55

+

3.80

:

:

: :

:6.3,;- 7p3D3

: : :

!6.3,: - 7 3,1

:

: 6037.70

:

: :

4.97

+

1.80

:

6054.86

: :

3.23

÷

1.35

: :

:

6069.00

:

4.59

~

1.80

:

: 3o :65 PI - 7p3Po

:

6073.46

:

6.27

÷

2.50

:

: 6 8 3 p ~ - 7p3D 2

:

6149.71

:

5~92

~

2.55

:

:6SlP?

- 7plD2

:

6154.60

:

~

5.0

:

7p3.1

:

6171.50

:

4.88

+

1.95

:

:

6203.64

:

0.788

~

0.35

:

:

6310.78

:

1.46

+

0.65

:

:

6354.35

:

0.845

~

0.35

:

:

:

: 3 o : 6 8 PI - 7p3DI :

] o 68 P! -

7plPi

-

I)

11.1

O T H E R DATA

0.875 (3) %

:

7p381

se~

:

0.85

:

- 7plV2

( 106

~ , A

TRANSITION

O.771 ( 4 )

1.4 (2)

Atomic transitionprobabilitiesfor Sn(I), Sn(II)and CI(I)lines

513

also been obtained in a multicomponent plasma containing At, Cr, O and CI, the parameters of which are close to ours. (23) The lowering of Tp leads to a moderate increase of the relative A values if the energy differences between the higher level of the standard line and those of other lines are not very large (i.e. - 1 eV). This case could arise for a number of metals. However, adjusting to an absolute scale could lead to systematic errors (for ionic lines), with their magnitude depending on the energy of the excited levels. Results of our measured transition probabilities are shown in the following tables. Table 2 contains the measured transition probabilities for the Sn(I) lines; Table 3 lists A values for the Sn(II) lines; both relative and absolute data are shown. Table 4 gives A values of the CI(I) lines. These values were obtained from mean values of line intensities by averaging over five measurements for each experimental condition. The transition probabilities for lines in the first two experimental sets were also averaged. The maximum error was evaluated by logarithmic differentiation. The estimated errors are about 40%, primarily because of inaccuracy in the A value for the standard line. Our A values for Sn(I) lines may be compared with the known result for the 5p 2 ISo-6s3p~° transition at 5631.71/~ and with theoretical data calculated by LAWRENCEO) and by GRU7.DEV(4) (Table 2). These latter data are lower by a factor of three than our experimental value, which is higher by a factor of 1.8 than the results obtained by CoRuss and BOZMANN.m Our A values for the principal and sharp series of Sn(II) may be compared with Table 3. Transitionprobabilitiesfor Sn(II)lines in the spectralrange5330-6844.~ :

:

:

TRANSITION

:

:

Amn

~, A

(IO7

sec-

1)

THIS WORK

:

:

:

Arelative

i62P1 .~ - 62D3 ~.

:

5332.56

:

271

+_

i

OTHER DATA

:

Aabsolute

:

30

:

8.60

+

3.10

Aabsolute

:

62P3/2 - 62D5/2

:

5561.95

:

372

~

37

:

11.80

+

4.0

i52D3/2 - 42F5/2

:

5588.92

:

267

~

37

:

8.47

+

3.56

=

i

:

5596.20

:

46.4 ~

5

:

i.47

+

0.54

:

14

:

2.80

!

1.0

:

25

:

8.11

~

2.9

:

~

3.64 ::

62P3/2 - 62D3/2

i52D5/2 - 42F5/2

5797.20

":52D5/2 - 42F7/2

:

".;6251/2 - 62P3/2

256

~

:: 6453.50

:: 383

~

34

:: 12.14

72S1/2

:

6761.45

:

IOO

+

I0

:

3.17

+ 0.98 :

162S1/2 - 6 2 P i / 2

:

6844.05

:

209

~

23

:

6.64

~

62P1/2

-

relativistic

5799.18

88.3

calculation

:

:

8 .18 (6)~

7.8 (5)

3.87 ( 6 ) I

2.12 :

6.6 (5)

6 . 99 (6)ffi

-

Table 4. Transitionprobabilitiesfor CIO)lines in the spectralrange6114-6435,~ : ."

(~

Vol.18,No. 5--D

TRANSITION

: :

~, A

: Amn (IO 7 :

sec- I)

: ;

+

0.12

:

14p4p° 5.+ / ~ - 5d4Ds.. /~

:

6114.37

:

14p4P°5/2

:

6140.21

:: 0.751

~

0.30

:

i 4p4p° 3 12 - 5d4D5/2

i

6194.72

:

+_

O.18

:

;4p4D°3 /2 - 5d2D5 /2

:

6341.66

:: 0.373

_+

O.15

::

~4p4D°7 /2 - 5d4F 9 /2

:

6398.63

:: 0.638

~

0.28

::

~4p4D°5/2 - 5d4FT/2

:

6434.73

:

~

O.15

:

5d4D7/2:

0.277

0.443

0.355

:

:

514

T. Wu~Ecand S. WEmo~

semi-empirical calculations of Kuslsz and MmDXLEK¢5>involving the deformation of the ionic core and with relativistic and non-relativistic calculations including exchange effects by MIGDXLEK.c6) For the 62S~r2-62p312 transition, a deviation by a factor of 1.5 is observed; good agreement exists for the 62Str~-62pt/2 and 62p~r2-72S~I2transitions (Table 3). As far as we know, no other data on CI(I) fines are available. The lowering of the plasma temperature by 570°K gives for Sn(I) lines an increase in A value of 10-15%; for an increase in absolute A values by about 23% for Sn(II) at 6453.50 ~ and 6844.05 ~ and about 33% for the remaining fines. The relative scale is affected by errors ranging from 3 to 5%, whereas the A values for Sn(II) at 6453.50 ~ and 6844.05 ~ decrease by about 14%. Finally, for CI(I) lines the A values are increased, as the result of lowering of the plasma temperature, by 5--6%. W e conclude that systematic errors resulting from deviations from LTE for argon in the plasma are primarily responsible for errors in the A values; an exception may occur for Sn(II) lines. REFERENCES 1. T. Wo~Ecand J. MUSmLOK,Astron, Astrophys. ,~, 405 (1976). 2. C. H. Cotuassand W. R. BozM~, NB$ Monograph. .~, Washington,D.C. (1962). 3. G. M. LAViR~CE,Astraphys. J. 14, 261 (196"/). 4. P. F. GXUZDEV,Opt. Spectrosc. 25, I (1968). 5. M. D. KUNISZand J. I~ODALXK,Acta Phys. PoL 145,715 (1974). 6. J. ~/[IGDALEK,JQSRT 16, 265 (1976). " 7. J. EULEX, Ann. Phys. ll, 202 (1953). 8. H. N. OLSEN, JQSRT 3, 305 (1965). 9. V. N. KOLESNIKOV and N. N. SOmOLEV, F~.. Prob. Spectrosc.l, I19 (1962). 10. D. B. Gmmvlcll and I. V. PODMOSlI~SKU, Opt. Spectrosc.lS, 319 (1%3). II. J. RIclrrn, Z. Astrophys.61, 57 (1965). 12. H. R. GmEM, SpectralLine Broadening by Plasma. Academic Press, New York (1974). 13. K. KATZONIS, Thesis Sci. Phys. Paris-Orsay, 1976 (unpublished). 14. H. W. DI~WlN and P. FELENBOK, Data For Plasma in Local Thermodynamic Equilibrium.Ganthier-VillarsEdit.,Paris.

(1965). 15. J. H/a.ENK^ and B. GI~SOWSKI, Astron.Astrophys.to be published. 16. H. GXUNDEL, 8eitr~geaus der Plasmaphysik 10, 455 (1970). 17. H. GRUNDF.L, Beitrdgeaus der Plasmaphysik II, I (1971). 18. W. R. LOCHTE-HOLTO~VEN, Plasma Diagnostics,North Holland, Amsterdam (1968). 19. J. MorrY, Th~se 3~ cycle, Paris VI, !973.

20. W. L. WmsE,M. W. Stem and B. M. MILES,NSRDS-NB$ 22, Washington,D.C. (1969). 21. H. W. D~WlN,High Pressures-High Temperatures2, 359 (1970). 22. N. P. PeNKINand J. M. SLAVSNAS,Opt. Spectrosc. 15, 154 (1963). 23. J. MUSI~LOKand T. WuJxc,Astron. Astraphys. to be published.