12 Measurement and Interpretation of Plutonium Spectra
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J. BLAISE Laboratoire Aimé Cotton, Centre de la Recherche Scientifique, Bat. 505, 91405 Orsay Cedex, France M. S. FRED, W. T. CARNALL, H. M. CROSSWHITE, and H. CROSSWHITE Argonne National Laboratory, Chemistry Division, Argonne, IL 60439
The atomic spectroscopic data available for plutonium are among the richest of any in the periodic system. They include high-resolution grating and Fourier-transform spectra as well as extensive Zeeman and isotope-shift studies. We summarize the present status of the term analysis and cite the configurations that have been identified. A least-squares adjustment of a parametric Hamiltonian for configurations of both Pu I and Pu II has shown that almost all of the expected low levels are now known. The use of a model Hamiltonian applicable to both lanthanide and actinide atomic species has been applied to the low configurations of Pu I and Pu II making use of trends predicted by ab initio calculations. This same model has been used to describe the energy levels of Pu in LaCl , and an extension has permitted preliminary calculations of the spectra of other valence states. 3+
3
In t h e f i f t e e n y e a r s s i n c e p u b l i c a t i o n o f an e a r l i e r s t a t u s r e p o r t on t h e a t o m i c s p e c t r a o f p l u t o n i u m and o t h e r actinide elements CO there h a s been steady progress, especially i n the parametric i n t e r p r e t a t i o n o f t h e energy levels. The a n a l o g y t o l a n t h a n i d e e l e c t r o n i c s t r u c t u r e h a s been more f i r m l y e s t a b l i s h e d , t h e r e l a t i o n s h i p s among a l l t h e e l e m e n t s o f t h e a c t i n i d e s e r i e s have been c l a r i f i e d , and a d e t a i l e d theory of the l a n t h a n i d e / a c t i n i d e c r y s t a l s p e c t r a has been d e v e l o p e d . The most t h o r o u g h l y a d v a n c e d o f t h e a c t i n i d e atomic s p e c t r o s c o p i c s t u d i e s a r e probably those f o r plutonium, so i t i s p a r t i c u l a r l y a p p r o p r i a t e t h a t i n t h i s 4 0 t h a n n i v e r s a r y y e a r we l o o k a g a i n a t where we s t a n d . Because o f t h e c l o s e r e l a t i o n s h i p between i o n i c e n e r g y l e v e l s i n t h e f r e e s t a t e and
0097-6156/83/0216-0173$07.50/0 © 1983 American Chemical Society
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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174
PLUTONIUM CHEMISTRY
in crystalline environments, the current s t a t u s of both experimental approaches i s presented, along with a b r i e f summary o f t h e g e n e r a l i z e d p a r a m e t r i c t h e o r y . A more t h o r o u g h d i s c u s s i o n o f t h e r e s u l t s o f t h e term a n a l y s i s f o r n e u t r a l plutonium (Pu I ) w i l l be g i v e n e l s e w h e r e (2) ; a complete l i s t i n g o f s p e c t r u m l i n e s and e n e r g y l e v e l s f o r Pu I and Pu I I w i l l be made a v a i l a b l e a s an Argonne N a t i o n a l L a b o r a t o r y R e p o r t (_3). A b b r e v i a t e d l i n e l i s t s were r e c e n t l y p u b l i s h e d by Conway and c o w o r k e r s (_4_), and some i n d e p e n d e n t work h a s a l s o been r e p o r t e d by S t r i g a n o v ( 5 ) . L e s s p r o g r e s s h a s been made i n interpreting the spectra of the higher valence states of plutonium i n condensed phases. The summary o f s t u d i e s p u b l i s h e d up t o ~1970 ( 6 ) i s s t i l l a r e l e v a n t d e s c r i p t i o n o f the s t a t u s o f t h i s work. Free-Ion
Spectra
The spectrum o f Pu was f i r s t p h o t o g r a p h e d i n 1943 by R o l l e f s o n and Dodgen ( 7 ) , who measured t h e w a v e l e n g t h s ( a n d i n t e n s i t i e s ) o f a b o u t 125 l i n e s . However, t h e f i r s t energy level a n a l y s i s d i d n o t come u n t i l 1959, when M c N a l l y and G r i f f i n (8), u s i n g a l o w - c u r r e n t dc a r c l o a d e d w i t h P u i na m a g n e t i c f i e l d o f 2.447 t e s l a s , f o u n d 7 o u t o f t h e 13 l e v e l s o f t h e g r o u n d terms 5 f 7 s F and F i n Pu I I and a l s o r e p o r t e d 84 high odd l e v e l s . (Only 73 o f t h e s e levels have been confirmed)· The g r o u n d m u l t i p l e t o f Pu I was s u b s e q u e n t l y e s t a b l i s h e d by Bovey and G e r s t e n k o r n ( 9 ) . C o m b i n i n g H a r w e l l Zeeman s p e c t r a ( f r o m an e l e c t r o d e l e s s d i s c h a r g e tube c o n t a i n i n g Pu i n a magnetic f i e l d of 3 t e s l a s ( 1 0 ) , w i t h t h e h y p e r f i n e s t r u c t u r e and i s o t o p e s h i f t measurements made a t L a b o r a t o i r e Aimé C o t t o n (LAC) f r o m a h o l l o w c a t h o d e w i t h a p h o t o e l e c t r i c F a b r y - P e r o t i n t e r f e r o m e t e r , these authors found t h e lowest f i v e l e v e l s o f 5f 7s F , a s w e l l a s 25 upper odd l e v e l s (9^, 11). Beginning i n 1961, t h e a n a l y s i s o f t h e p l u t o n i u m s p e c t r a became a j o i n t project carried out by spectroscopists from three laboratories : Argonne N a t i o n a l L a b o r a t o r y ( A N L ) , Lawrence L i v e r m o r e N a t i o n a l L a b o r a t o r y ( L L N L ) and LAC. In the early s t a g e s o f t h e terra a n a l y s i s , when s e p a r a t e d i s o t o p e s became a v a i l a b l e i n s u f f i c i e n t q u a n t i t y f o r s p e c t r o s c o p i c use, s p e c i a l e l e c t r o d e l e s s t u b e s were p r e p a r e d f o r p a r t i c u l a r e x p e r i m e n t s . One, p r e p a r e d by E. Worden o f LLNL, c o n t a i n e d 8 8 % P u f o r use w i t h t h e ANL 3 0 - f o o t Paschen-Runge s p e c t r o g r a p h and t h e 2.4 t e s l a magnet. The t h o u s a n d s o f Zeeman p a t t e r n s ( a n example i s shown i n F i g . 1 ) , o b t a i n e d w i t h t h i s t u b e were e s s e n t i a l f o r further progress i n the a n a l y s i s . The s m a l l r e s i d u a l amount o f 23 9 p i p e r m i t t e d i s o t o p e - s h i f t measurements t o s u p p l e m e n t t h e more a c c u r a t e i n t e r f e r o m e t r i c measurements o f G e r s t e n k o r n ( 11 ) and S t r i g a n o v and K o r o s t y l e v a ( 1 2 , 1 3 , 1 4 ) . Subsequent s p e c t r o g r a m s t a k e n w i t h t u b e s p r e p a r e d by F. S. Tomkins a t ANL 2 3 9
6
8
6
2 3 9
6
2
7
2 i + 0
u
a
s o
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
BLAISE ET AL.
Measurement and Interpretation of Pu Spectra
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12.
F i g u r e 1. Zeeman p a t t e r n teslas.
f o r Pu I
at
8534 A
photographed
at
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
2.4
175
176
PLUTONIUM CHEMISTRY
2 3 9
with mixtures of P u and e v e n i s o t o p e s 238-244 ( a s t h e y became available as separated s p e c i e s ) were measured by G e r s t e n k o r n a t LAC. I n 1970 t h e s p e c t r a o f P u and o f a m i x t u r e o f t h e 240, 242, and 244 i s o t o p e s were r e c o r d e d by F o u r i e r - t r a n s f o r m s p e c t r o s c o p y a t LAC up t o 3.59 pm. A portion o f one o f t h e s e r e c o r d i n g s i s shown i n F i g . 2. The h i g h e r resolution made available by these experiments and the c o n n e c t i o n s between l o w l e v e l s made p o s s i b l e by t h i s e x t e n s i o n i n t o the i n f r a r e d g r e a t l y advanced the a n a l y s i s . F o r e a s i e r r e f e r e n c e t o e a r l i e r work t h e s h i f t f o r ( 2 3 9 240) was a d o p t e d as t h e r e f e r e n c e f o r t a b u l a t i o n and where n e c e s s a r y d e r i v e d f r o m t h e (240-244) i s o t o p e s h i f t by d i v i d i n g t h e l a t t e r by 2.531, a c o n s t a n t f a c t o r d e t e r m i n e d by B l a i s e et a l . ( 15). Over 9500 i s o t o p e s h i f t s have now been m e a s u r e d , 50% o f them i n t h e i n f r a r e d . The number o f e n e r g y l e v e l s f o u n d t o d a t e , w i t h t h e a i d o f t h e Zeeman e f f e c t and t h e i s o t o p e s h i f t d a t a , i s 605 e v e n and 586 odd l e v e l s f o r Pu I and 252 even and 746 odd f o r Pu I I . The quantum number J has been d e t e r m i n e d f o r a l l t h e s e l e v e l s , t h e Lande g - f a c t o r f o r most o f them, and t h e i s o t o p e s h i f t f o r a l m o s t a l l o f t h e Pu I l e v e l s and f o r h a l f o f t h o s e o f Pu I I . Over 31000 l i n e s have been o b s e r v e d o f w h i c h 52% have been c l a s s i f i e d as t r a n s i t i o n s between p a i r s o f t h e above l e v e l s . These r e p r e s e n t 23 d i s t i n c t e l e c t r o n c o n f i g u r a t i o n s . The m a i n p r o b l e m s i n t h e s e v e r y complex s p e c t r a a r e ( 1 ) t o f i n d t h e l e v e l s , and ( 2 ) t o a s s i g n t h e l e v e l s t o t h e p r o p e r configuration. I n t h e a b s e n c e o f c o n f i g u r a t i o n i n t e r a c t i o n one can e s t i m a t e t h e i s o t o p e s h i f t f o r various configurations, t a k i n g i n t o account t h e s c r e e n i n g o f t h e 7s e l e c t r o n c h a r g e d e n s i t y a t t h e n u c l e u s by t h e 5 f , 6 d , and 7p e l e c t r o n s ( 1 6 ) . Comparison of these e s t i m a t e s w i t h e x p e r i m e n t a l o b s e r v a t i o n s i s an i m p o r t a n t f i r s t s t e p i n i d e n t i f y i n g n u m e r i c a l e n e r g y l e v e l s w i t h t h e i r quantum m e c h a n i c a l counterparts. Computations of t h e c e n t r a l e l e c t r o n d e n s i t y , [4πψ (0)] have been r e p o r t e d using both the n o n - r e l a t i v i s t i c ( 1 7 ) and r e l a t i v i s t i c ( 18) Hartree-Fock procedures. When t h e i s o t o p e s h i f t c h a r a c t e r i s t i c of the l i n e s b e l o n g i n g to a p a r t i c u l a r c o n f i g u r a t i o n i s p l o t t e d against the r e l a t i v i s t i c value f o r 4πψ (0), the r e s u l t i n g r e l a t i o n s h i p i s s e e n t o be a l i n e a r f u n c t i o n , F i g . 3 ( 1 8 ) . Thus f a r , we have i d e n t i f i e d levels belonging t o 14 d i f f e r e n t c o n f i g u r a t i o n s o f Pu I and t o 9 c o n f i g u r a t i o n s i n Pu I I . The l o w e s t l e v e l s o f t h e s e c o n f i g u r a t i o n s a r e g i v e n i n T a b l e I a l o n g w i t h Lande g - f a c t o r s and t h e e x p e r i m e n t a l i s o t o p e shifts. The l a t t e r v a l u e s a r e a v e r a g e s and have changed i n magnitude somewhat as more experimental data has been analyzed. T h i s c a n be s e e n by c o m p a r i s o n o f v a l u e s i n T a b l e I with earlier tabulations such as shown in Fig.7 of r e f e r e n c e 1. S e v e r a l l e v e l s s h o w i n g anomalous i s o t o p e s h i f t s a r e p e r t u r b e d by n e a r b y l e v e l s w i t h t h e same J b u t w h i c h however b e l o n g t o a n o t h e r c o n f i g u r a t i o n . F o r a more d e t a i l e d
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2 i + 0
2
2
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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BLAISE ET AL.
Measurement and Interpretation of Pu Spectra
—I—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—j—ι—ι—ι—ι—j—ι—ι—ι—ι—ι—ι—ι—Γ 8028
8029
8030
8031
8032
8033
σ (cm") 1
F i g u r e 2. Spectra of a mixture of > ^Pu by F o u r i e r - t r a n s f o r m s p e c t r o s c o p y . y
z
isotopes
recorded
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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178
PLUTONIUM CHEMISTRY
9001
7537900
7538000
7538100
7538200
7538300
7538400
F i g u r e 3. I s o t o p e s h i f t f o r v a r i o u s c o n f i g u r a t i o n s i n Pu I p l o t t e d as a f u n c t i o n o f t h e c e n t r a l e l e c t r o n d e n s i t y , 4 π ψ ( 0 ) . 2
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
6
7
2
5f
7
5f 7p
6
5f 6d
6
5f 7s
6
Pu I I
7
6
l/2
3
7/2
-ι Ο
J
h/2
22039
12008
0
25192
l/2
31573
5f 7s
B
33071
5f 7s8s
6
15449
31711
5f 7s7p
2
0
13528
Ε
0.344
-0.019
3.150
1.768
2.403
0.673
-
0.200
-0.590
-
g
(0)
287
77
381
273
446
293
336
115
253
465
IS
2
4
2
5f 6d 7s
5f 6d7p
5
5f 7s7p
5
5
5f 6d
5f 6d7s
5
5 f 7s
4 2 2 5 f 6d 7s
5
5/2
9/2
5/2
9/2
M. 11/2
J
[
J
^7/2
37641
33793
30956
17297
8710
8199
36051
39618
20828
17898
?
37415
Λ
6314 14912
5f 6d7s8s
z
5f 6d7s7p 5 2 5 f 6d 7p
5
3
3
5 2 5f 6d7s 5 2 5 f 6 d 7s 5 3 5 f 6d 5 2 5 f 7s 7p
0.70
0.800
0.646
0.494
0.308
0.414
0.830
0.270
0.980
0.352
0.450
0.496
0.487
g
The L o w e s t L e v e l o f E a c h C o n f i g u r a t i o n o f P u I and Pu I I w i t h t h e i r C o r r e s p o n d i n g g - V a l u e s and E x p e r i m e n t a l I s o t o p e S h i f t s (E i n cm"~l and I S i n 10"" 3 c m ~ l ) .
5f 6d7p
6
5f 6d
6
5f 6d7s
6
5 f 7s
^
Pu I
Table I .
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813
208
424
242
555
896
535
503
403
467
698
488
653
IS
Lande
180
PLUTONIUM CHEMISTRY
d i s c u s s i o n o f t h e dependence o f i s o t o p e s h i f t s on t h e e l e c t r o n c o n f i g u r a t i o n o c c u p a n c y , see R e f e r e n c e ( 1 8 ) . A c c o r d i n g to the s y s t e m a t i c r e l a t i o n s h i p s d e v e l o p e d by B r e w e r ( 1 9 ) , t h e s t i l l m i s s i n g f d c o n f i g u r a t i o n i n Pu I s h o u l d b e g i n a r o u n d 27000 ± 5000 cm" , and t h e l e v e l 5 f ( S 7 / 2 o f Pu I I i s p r e d i c t e d t o o c c u r a t 14000 ± 8000 cm" . A f u r t h e r c h e c k on t h e c o n f i g u r a t i o n a s s i g n m e n t s made t o d a t e can be o b t a i n e d by s y s t e m a t i c a l l y c o m p a r i n g t h o s e g i v e n i n Table I f o r the lowest l e v e l s w i t h analogous ones f o r o t h e r elements, as i n F i g s . 4 and 5 f o r a l l t h e known a c t i n i d e configurations. To b e t t e r see t h e t r e n d s a c r o s s t h e s e r i e s f o r g i v e n c o n f i g u r a t i o n t y p e s we have changed t h e e n e r g y r e f e r e n c e from the e x p e r i m e n t a l zero (ground s t a t e ) t o the lowest l e v e l of a p a r t i c u l a r c o n f i g u r a t i o n type. In the l e f t h a l f of F i g . 4, we have c h o s e n 5 f 7 s as t h e r e f e r e n c e . C o n f i g u r a t i o n s w i t h two v a l e n c e e l e c t r o n s t h e n t e n d t o show a f l a t t e r , l e s s i r r e g u l a r d i s p l a y than i f r e f e r e n c e d a g a i n s t a ground s t a t e with v a r i a b l e c o n f i g u r a t i o n type. Configurations with three or f o u r v a l e n c e e l e c t r o n s show a s t e e p , but a l s o more r e g u l a r , r i s e as t h e f - s h e l l c o l l a p s e p r o g r e s s e s . In the a l t e r n a t e d i s p l a y on t h e r i g h t , 5 f ^ " 6 d 7 s l o w e s t l e v e l s were t a k e n as the r e f e r e n c e . T r i v a l e n t c o n f i g u r a t i o n s a r e now relatively f l a t , w i t h the former r e f e r e n c e 5 f ^ 7 s c o n f i g u r a t i o n s showing a steep fall and 5f " 6d 7s a less steep r i s e . Not a l l c o n f i g u r a t i o n types are p l o t t e d i n both diagrams. Similar d i s p l a y s o f Pu I I l o w e s t l e v e l s a r e p l o t t e d i n F i g . 5, w i t h 5 f 7 s and 5 f ^ " 7 s being chosen f o r a l t e r n a t i v e r e f e r e n c e s . A l l the assignments g i v e n i n Table I are c o n s i s t e n t w i t h these diagrams· The f i r s t and second s p e c t r a o f p l u t o n i u m a r e p r o b a b l y t h e most t h o r o u g h l y s t u d i e d o f any i n t h e p e r i o d i c t a b l e i n s o f a r as e x p e r i m e n t a l d e s c r i p t i o n o f t h e o b s e r v e d s p e c t r a and t h e t e r m analysis i s concerned, but a detailed quantum mechanical treatment has been h a n d i c a p p e d by t h e i r great complexity. F o r t u n a t e l y , t h e l o w e s t odd and l o w e s t even c o n f i g u r a t i o n s f o r both Pu I and Pu I I a r e r e l a t i v e l y s i m p l e , and parametric s t u d i e s of the lowest l e v e l s of the 5 f 7 s , 5 f 6 d 7 s and 5 f 7 s 8 s c o n f i g u r a t i o n s i n Pu I ( 2 0 , 21) and 5 f 7 s i n Pu I I (21) were p e r f o r m e d a t an e a r l y s t a g e . A "generalized" parametric s t u d y (22) o f t h e 5 f 7 s and 5 f ^ 7 s c o n f i g u r a t i o n s i n t h e f i r s t and second s p e c t r a of the actinides has shown a smooth v a r i a t i o n of a l l the u s u a l parameters of the core 5 f . The o n l y m i s s i n g l e v e l b e l o w 20000 cm" i n 5 f 7 s o f Pu I has now been f o u n d , 107 cm" lower than p r e d i c t e d . Some r a t h e r h e a v i l y - t r u n c a t e d v e r s i o n s o f t h e more c o m p l e x configurations have been used a t ANL to a s s i s t in level identifications. A summary o f t h e f i t t e d p a r a m e t r i c r e s u l t s for t h e l o w e s t c o n f i g u r a t i o n s o f Pu I and Pu I I i s g i v e n i n Table I I . In some c a s e s c o n f i g u r a t i o n mixing has been included. The numbers e n c l o s e d i n p a r e n t h e s e s f o l l o w i n g t h e 5
3
0
1
7
8
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1
N
2
1
2
2
N
N
1
2
2
2
2
6
2
6
5
2
6
N
2
N
1
6
2
1
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Measurement and Interpretation of Pu Spectra
BLAISE ET AL.
181
AnIf "'d
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N
f 7ds _ 7
f d7s8p_
2
f%7ffls„-^-*="-—5f "'6d7s8s
3
N
f 7s8s—
/
3
/*
,3 2_ S
fffi.
ft2-/fV- f S - f V - f f V 7
2
f'°S - f " s - ^ S f ^ S 2
2
5f -'6d 7p N
2
θ|
2
f ds i 7
2
3/
f ds* Th Pd
2
4
5
6
7
8
9
10
II
12
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Ν
I
2
3
4
5
Ac
Th
Po
U
Np
6 \
2
Ac
Pu
'»
7
8
9\
10
II
Cm
8k ;
Cf
Es
fV
f°s
2
F i g u r e 4. Systematic v a r i a t i o n of the lowest-energy l e v e l s i n a g i v e n c o n f i g u r a t i o n f o r An I p l o t t e d as a f u n c t i o n o f N, where Ν = Ζ - 8 8 .
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Ν
PLUTONIUM CHEMISTRY
182
An H f
Ν
An llf
(lO^m-'l
N-l
(I0 cn 3
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40
f d s 4
-
2
f dp5
f sp5
f sp f s£^^—5f "'7s7p 8
2 5
h
^
7
-v--5f 6d7s N ,
O h
»s-
J
A 2 - A t
f s~ 2
I I
Ac
2 Th
I 3
I 4
Ρα
f s~
L 5
U
f s-/f s-f
7
Np
8
J 6 Pu
7
9
1 8
Am
Cm
I O
— / ^
s-f"s--^5f 7s N
I
I
I
9
10
II
Bk
N
Cf
Es
L
-10
J
L
_L_J
I
I
1
I
12
I
2
3
4
5
6
7
8
9
Fm
Ac
Th
Pa
U
Np
Pu
Am
Cm
Bk
I 10 Cf
F i g u r e 5. Systematic v a r i a t i o n of the lowest-energy l e v e l s i n a g i v e n c o n f i g u r a t i o n f o r An I I p l o t t e d as a f u n c t i o n o f N, where Ν = Ζ - 88.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
L II Es
Ν
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Also:
3
2
2
3
5
4
3
2
1
1
2
a
3
4
65466(1076) 47578(1373) [36164] [27124] [32.55] [-750] [1300] 2100(26) 897(42) 9469(593) 11108(987) 3977(202) [902] 9148(638) [1000] 985(549) 2819(93) 3684(549) -8260(1715)^ -3782(1291)
45122(189) 45114(624) 31656(1174) [24452] [32.55] [-652] [1200] 2063(20)
6
f ds
Pu I 2 a
6
52342(115) [49300] [39500] 27460(739) [35] [-900] [1100] 2233(12) 1412(28) 14973(335) [11000] 6357(113) 614(355) 8293(304) [2000] 6081(307)
5
f ds
7
b
S
8
60844(169) [43500] [34000] [24000] [31.5] [-750] [1300] 2084(26) 1429(82) 18805(635) [12000] 2266(594) [1000] 10840(823) [1000] [7500]
6
f d«
2
5
f ds
a
= 0.41, M
4
= 0.29,
57794(328) 49230(1243) 37215(1468) [27918] [32.55] [-652] [1200] 2263(11) 1677(39) 20468(445) 14251(1090) 9027(159) 387(932) 9452(528) 1903(808) 8515(661) 2353(93) 7838(386) -6135 (508)° -564(537) 48696(215) 49066(770) 39640(719) 26946(785) [32.55] [-652] [1200] 2275(27)
f s
Pu I I
= 352, M° = 0.75, M
2498(45)
43311(221) 32103(536) 23201(297) 53.5(1.5) -1261(84) 2035(140) 2079(11)
6
f Z>
T = 200, T = 30, T =,11, T = - 3 6 8 , T « 389, T Ρ = 1334, Ρ = 1000, Ρ = 667, a l l f i x e d . From R e f e r e n c e 22. q Ν 2 Ν C o n f i g u r a t i o n m i x i n g b e t w e e n f s and f d s .
a
6
2
1
2
EAV F F* F α 3 Ύ Çf ζά F (fd) F* G G G G G G (fs) G (ds) R (fd,fs) R (fd,sf)
r
6 2 f s
a
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184
PLUTONIUM CHEMISTRY
t a b u l a t e d values represent the s t a t i s t i c a l e r r o r s a s s o c i a t e d w i t h t h a t p a r t i c u l a r parameter v a l u e . A number e n c l o s e d by s q u a r e b r a c k e t s i s one f o r w h i c h t h a t p a r a m e t e r was h e l d f i x e d d u r i n g the l e a s t - s q u a r e s f i t t i n g procedure. C a l c u l a t i o n s such as these have been i n v a l u a b l e i n d e f i n i n g the quantumelectronic nature of the empirical levels; the derived e i g e n v e c t o r s a r e u s e d t o compute g - v a l u e s and i s o t o p e s h i f t s f o r d i r e c t c o m p a r i s o n w i t h e x p e r i m e n t a l measurements as w e l l as f o r more i n d i r e c t a n a l y s e s o f h y p e r f i n e s t r u c t u r e p a r a m e t e r s (23). Because of the stability of the f - o r b i t a l s i t is possible to draw a strong parallel among their atomic p a r a m e t e r s and analogous parameters from s t u d i e s of other actinide and lanthanide cases. In fact, Hartree-Fock c a l c u l a t i o n s o f t h e a s s o c i a t e d r a d i a l i n t e g r a l s shown i n T a b l e s I I I A and Β f o r some c a s e s o f i n t e r e s t h e r e , t o g e t h e r w i t h appropriate systematic c o r r e c t i o n s deduced from e m p i r i c a l s t u d i e s , can be u s e d as t h e b a s i s o f a p a r a m e t r i c model w h i c h embraces a l l o f t h e a c t i n i d e and l a n t h a n i d e s p e c t r a so f a r subjected to d e t a i l e d study. These c o r r e c t i o n s t a k e two forms: (1) a numerical c o r r e c t i o n to the Hartree-Fock e s t i m a t e s , p a r t i a l l y a c c o u n t i n g f o r the masking of parameters w h i c h i s one c o n s e q u e n c e o f t h e breakdown o f t h e singlec o n f i g u r a t i o n a p p r o x i m a t i o n and ( 2 ) i n t r o d u c t i o n o f a d d i t i o n a l ( e f f e c t i v e ) H a m i l t o n i a n o p e r a t o r s w h i c h have no meaning i n a s i n g l e - c o n f i g u r a t i o n a p p r o x i m a t i o n but w h i c h t o a l a r g e e x t e n t mimic the e f f e c t s of i n t e r a c t i o n s w i t h o t h e r c o n f i g u r a t i o n s w i t h o u t i n c r e a s i n g the s i z e s of the m a t r i c e s i n v o l v e d . Because these c o r r e c t i o n s to the Hartree-Fock estimates, and the e m p i r i c a l parameters a s s o c i a t e d w i t h e f f e c t i v e o p e r a t o r s , are n e a r l y i n d e p e n d e n t of t h e p a r t i c u l a r i o n u n d e r s t u d y , i t i s p o s s i b l e t o make r e a s o n a b l y a c c u r a t e e s t i m a t e s o f plutonium parameters i n advance of the d e t a i l e d a n a l y s i s . I n d e e d , as nearly as we have been a b l e to determine, none o f the e f f e c t i v e - o p e r a t o r parameters are s i g n i f i c a n t l y d i f f e r e n t i n analogous c r y s t a l / f r e e - i o n comparisons. As a c o n s e q u e n c e , we have used t h e g e n e r a l p a r a m e t r i c model t o g i v e e s t i m a t e s where e m p i r i c a l data are i n s u f f i c i e n t , i n attempts to i n t e r p r e t both c r y s t a l and f r e e - i o n cases. In s p i t e of the c o m p l i c a t i o n s b r o u g h t a b o u t by t h e e f f e c t s o f t h e c r y s t a l - f i e l d i n t e r a c t i o n , the f a c t that i n c r y s t a l spectra only t r a n s i t i o n s between l e v e l s o f 5 f i t s e l f a r e e n c o u n t e r e d a t l o w e n e r g i e s has l e d t o a g r e a t s i m p l i f i c a t i o n o f t h e p r o b l e m s o f i d e n t i f i c a t i o n and interpretation. The c o n d e n s e d - p h a s e s p e c t r a o f p l u t o n i u m i n the tetravalent, ( I V ) , through ( V I I ) o x i d a t i o n s t a t e s are known, but theoretical intepretation of the observed t r a n s i t i o n s i s not as h i g h l y d e v e l o p e d as t h a t c h a r a c t e r i s t i c of P u . However, s e v e r a l g e n e r a l s t a t e m e n t s r e g a r d i n g the e l e c t r o n i c s t r u c t u r e o f Pu i n c o n d e n s e d phase can be made as a r e s u l t o f r e c e n t work. The s u b s e q u e n t d i s c u s s i o n , t h e r e f o r e , r e p r e s e n t s a c o n t i n u a t i o n of t h a t of Pu I and Pu I I s p e c t r a , N
3 +
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
12.
BLAISE ET AL.
Table I I I ( A ). Spectrum
Measurement and Interpretation of Pu Spectra
HFR
a
Values for 5 f
Configuration
I
5 f 7s 5
5f 6d7s
2
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F
F
4
6
ζ
M°
71461
46094
33638
2230
0.75
76279
49543
36268
2422
0.84
70790
45619
33280
2215
0.74
5f 7s
6
71900
46400
33867
2239
0.76
5 f 7s
77274
50260
36815
2249
0.86
5
76452
49664
36360
2426
0.85
6
5f 6d
70980
45747
33374
2217
0.74
5f 6d7s
III
Cores of Pu C o n f i g u r a t i o n s .
6
5f 6d7s II
F
2
N
6
72563
46868
34220
2255
0.77
5
5f 6d
76820
49926
36558
2436
0.85
5f
IV
5f
5
78223
50942
37335
2479
0.88
V
5f
4
82908
54356
39965
2679
0.98
VI
5f
3
86982
57347
42285
2914
1.09
VII
5f
2
90625
60037
44381
3130
1.19
Computed u s i n g H a r t r e e - F o c k methods a n d i n c l u d i n g a n a p p r o x i m a t e r e l a t i v i s t i c correction (24).
Table I I I ( B ) .
Parameter
HFR
a
Pu I 5 2 5 f 6d7s 1695
£d
Values f o rInequivalent-Electron Interactions Pu I
Pu I I 5
5f 6d7s
5f 6d7s
985
1976
6
Pu I I 6
5f 6d
Pu I I I 5
5f 6d
1418
2255
24469
17687
27225
22959
29649
4
12649
8871
14292
11913
15773
X
14187
11109
15918
14713
17378
3
10326
7588
11701
10257
12918
3
2995
3696
2
19822
21708
2
F (fd) F (fd) G (fd) G (fd) G (fs) G (ds)
d
"Computed u s i n g H a r t r e e - F o c k methods a n d i n c l u d i n g a n a p p r o x i m a t e r e l a t i v i s t i c correction (24).
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
185
186
PLUTONIUM CHEMISTRY
beginning with consideration of divalent plutonium, and a d d r e s s i n g the condensed-phase s p e c t r a at i n c r e a s i n g s t a g e s of ionization.
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Crystal
Spectra
I n what f o l l o w s we b r i e f l y r e v i e w some o f t h e previous a t t e m p t s t o a n a l y z e t h e a v a i l a b l e s p e c t r a o f p l u t o n i u m (6_) · In a d d i t i o n , we e s t i m a t e e n e r g y l e v e l p a r a m e t e r s t h a t i d e n t i f y a t least the gross features c h a r a c t e r i s t i c of the spectra of p l u t o n i u m i n v a r i o u s v a l e n c e s t a t e s i n the lower energy range where i n most c a s e s , s e v e r a l i s o l a t e d a b s o r p t i o n bands can be discerned. The method u s e d was based on our i n t e r p r e t a t i o n o f t r i v a l e n t a c t i n i d e and l a n t h a n i d e s p e c t r a , and the g e n e r a l i z e d model referred to earlier i n the discussion of free-ion spectra. As was t h e c a s e w i t h l a n t h a n i d e c r y s t a l s p e c t r a ( 2 5 ) , we found that a systematic analysis could be developed by e x a m i n i n g d i f f e r e n c e s , ΔΡ, between experimentally-established a c t i n i d e p a r a m e t e r v a l u e s and t h o s e computed u s i n g H a r t r e e - F o c k methods w i t h t h e i n c l u s i o n o f r e l a t i v i s t i c c o r r e c t i o n s ( 2 4 ) , as i l l u s t r a t e d i n T a b l e IV f o r A n . C r y s t a l - f i e l d e f f e c t s were a p p r o x i m a t e d b a s e d on s e l e c t e d p u b l i s h e d r e s u l t s . By f o r m i n g t a b u l a t i o n s s i m i l a r t o T a b l e IV f o r 2 , 4 , 5 and 6 spectra, t o t h e e x t e n t t h a t any e x p e r i m e n t a l d a t a were a v a i l a b l e t o t e s t t h e p r e d i c t i o n s , we f o u n d t h a t t h e ΔΡ-values f o r P u provided a good s t a r t i n g point f o r a p p r o x i m a t i n g the structure of plutonium spectra in other valence states. However, a d j u s t m e n t s were r e q u i r e d f o r e a c h i n d i v i d u a l o x i d a t i o n s t a t e . I n a d d i t i o n t o t r a n s i t i o n s w i t h i n the 5 f ^ c o n f i g u r a t i o n w h i c h c h a r a c t e r i z e the l o w e r e n e r g y s t a t e s i n t h e f o l l o w i n g d i s c u s s i o n , the e n e r g y o f o n s e t of f+d transitions is an i m p o r t a n t v a r i a b l e which s t r o n g l y i n f l u e n c e s the n a t u r e of the spectra. F o r e x a m p l e , i n t e n s e a b s o r p t i o n bands c h a r a c t e r i s t i c o f f-κΐ t r a n s i t i o n s i n t h e u l t r a v i o l e t r a n g e o f the P u ( a q u o ) s p e c t r u m , F i g . 6, c o m p l e t e l y mask t h e p r e s e n c e o f weaker f * f transitions. The f i r s t f+d t r a n s i t i o n i s s h i f t e d t o w a r d h i g h e r energies w i t h i n c r e a s i n g v a l e n c y , and w i t h i n c r e a s i n g a t o m i c number w i t h i n a s i n g l e o x i d a t i o n s t a t e . P r e d i c t i o n of the energy l e v e l s t r u c t u r e f o r P u (5f ) i s o f p a r t i c u l a r i n t e r e s t s i n c e no s p e c t r a f o r t h i s v a l e n c e s t a t e o f Pu have been r e p o r t e d . On t h e b a s i s o f what i s known o f t h e s p e c t r a of A m (26), C f ( 2 7 ) , and E s ( 2 8 ) , there appears to be e v i d e n c e f o r a v e r y s m a l l c r y s t a l - f i e l d s p l i t t i n g o f t h e free-ion levels. Such e v i d e n c e e n c o u r a g e s use o f a f r e e - i o n c a l c u l a t i o n i n t h i s p a r t i c u l a r case. The parameter values s e l e c t e d a r e i n d i c a t e d i n T a b l e V. Based on the systematics g i v e n by Brewer ( 1 9 ) , t h e f i r s t f-xi t r a n s i t i o n s h o u l d occur n e a r 11000 cm" , so t h e f * f t r a n s i t i o n s a t h i g h e r energies w o u l d be e x p e c t e d t o be at least partially obscured. A 3 +
+
+
+
+
3 +
3 +
2 +
2 +
2 +
2 +
1
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
6
12.
BLAISE ET AL.
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Table IV.
Measurement and
Interpretation of Pu Spectra
C o m p a r i s o n o f E n e r g y L e v e l P a r a m e t e r s Computed U s i n g H a r t r e e - F o c k M e t h o d s and Those E v a l u a t e d f r o m F i t t i n g Experimental Data f o r A n ^ ( a l l i n c n f l ) . +
U
Np
Pu
Am
2
a
71442
74944
78223
81346
2
b
39715
44907
48670
51800
31727
30037
29553
29546
4
46370
48733
50942
53044
4
F (FIT)
33537
36918
39188
41440
ΔΡ
12833
11815
11754
11604
6
33981
35684
37335
38905
6
F (FIT)
23670
25766
27493
30050
ΔΡ
10248
9918
9842
8855
(HFR)
1898
2182
2479
2792
ζ(FIT)
1623
1938
2241
2580
275
244
238
212
F (HFR) F (FIT) ΔΡ
F (HFR)
F (HFR)
ζ
ΔΡ
Computed u s i n g H a r t r e e - F o c k methods and i n c l u d i n g a n r e l a t i v i s t i c correction (24).
approximate
Computed by f i t t i n g t o e x p e r i m e n t a l d a t a .
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
187
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PLUTONIUM CHEMISTRY
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
12.
BLAISE ET AL.
k
ΔΡ = F ( o r
Measurement and T a b l e V. Estimated C) - F (or c ) a
k
H F R
F
2
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Pu *
Pu^
26500 14000 10000 200
AF^ AF Δζ 6
Interpretation of Pu
Y
P
T
b
Spectra
Values of f o r Pu ( a l l i n c m " ) . 1
+
28000 13000 9200 350
Pu5+
Pu6+
30000 15000 10000 350
30000 16000 11000 350
°The v a l u e s o f F ( o r c ) are given i n Table I I I A . In each case the f o l l o w i n g a d d i t i o n a l f r e e - i o n parameters were included in the calculation, (25): α = 35, β = -1000, γ = 1200. Τ = 200, Τ = 50, Τ = 100, Τ = -300, Τ = 400, Τ 350. Ρ = 1200, Ρ * = 900, Ρ = 600, Μ° = .767, Μ = .423, Μ * = .293, a l l i n cm" . H
2
8
F
R
3
2
4
1
1
6
7
6
2
1
p r e d i c t e d e n e r g y l e v e l scheme i s g i v e n i n F i g . 7. The g r o u p o f bands computed t o l i e n e a r 10000 cm" may be u s e f u l i n any e f f o r t t o c h a r a c t e r i z e compounds i n w h i c h t h i s v a l e n c e s t a t e i s stabilized. The s p e c t r a o f P u : L a C l 3 ( 2 9 ) and i s o s t r u c t u r a l PUCI3 ( 30) have been e x a m i n e d and t h e e n e r g y - l e v e l a n a l y s i s has b e e n refined using extensive c r y s t a l - f i e l d data. Consequently, the r e s u l t s i n c l u d e d i n T a b l e IV a r e w e l l e s t a b l i s h e d . As a l r e a d y i n d i c a t e d , t h e y s e r v e as one b a s i s f o r e s t i m a t i n g p a r a m e t e r s for higher-valent species. Attempts have been made t o a n a l y z e the energy level s t r u c t u r e of P u ^ compounds i n terms o f a f r e e - i o n m o d e l , b u t , w i t h i n c r e a s i n g m e t a l - i o n valence the c r y s t a l - f i e l d splitting also increases s i g n i f i c a n t l y . Frequent o v e r l a p i n energies of crystal-field levels belonging to s e v e r a l d i f f e r e n t parent f r e e - i o n s t a t e s i s p r e d i c t e d . For a r e a l i s t i c c a l c u l a t i o n , the c r y s t a l - f i e l d must be d i a g o n i z e d s i m u l t a n e o u s l y w i t h t h e f r e e i o n p a r t s of the i n t e r a c t i o n . I n a d d i t i o n , many Pu*"*" compounds e x h i b i t an i n v e r s i o n symmetry a t t h e Pu ** s i t e . In such cases t h e s p e c t r u m i s d o m i n a t e d by v i b r o n i c t r a n s i t i o n s . The z e r o phonon t r a n s i t i o n s a r e f o r b i d d e n i n t h e l i m i t of i n v e r s i o n symmetry but may a p p e a r w e a k l y i f t h e r e i s any significant d i s t o r t i o n away f r o m t h e symmetry. T h u s , n o t o n l y must t h e effects of the crystal-field interaction be treated s i m u l t a n e o u s l y w i t h t h e f r e e - i o n i n t e r a c t i o n s , but t h e a n a l y s i s can be e x c e e d i n g l y c o m p l e x . T h e r e i s an i n t e r e s t i n g s i m i l a r i t y i n t h e c h a r a c t e r o f t h e s o l u t i o n a b s o r p t i o n s p e c t r a of the i s o e l e c t r o n i c i o n s N p and Pu** e v e n t h o u g h t h e a b s o r p t i o n bands i n P u ^ are a l l s h i f t e d toward higher energies due to increases in both the e l e c t r o s t a t i c ( F ) and s p i n - o r b i t (ζ) p a r a m e t e r s , T a b l e V I . We have a l s o examined t h e s p e c t r a o f c o m p l e x a l k a l i - m e t a l : P u ( I V ) 1
3 +
+
1
1
3 +
+
+
k
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
189
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190
PLUTONIUM CHEMISTRY
U Np Pu Am F i g u r e 7. P r e d i c t e d f r e e - i o n energy l e v e l s i n t h e 5 f - c o n f i g u r a t i o n of U + through A m and t h e o v e r l a p p i n g r a n g e o f t h e N^ N-l transitions. N
2
5 f
5 f
2 +
d
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
12.
BLAISE ET AL.
Measurement and
191
Interpretation of Pu Spectra
f l u o r i d e s ( 3 1 ) , and f i n d a s t r o n g s i m i l a r i t y i n t h e e n e r g i e s a t w h i c h many o f t h e a b s o r p t i o n bands a r e o b s e r v e d compared t o those for Pu (aquo). Thus, while the crystal-field i n t e r a c t i o n of A n i s l a r g e r t h a n t h a t i n A n , some o f t h e c h a r a c t e r i s t i c s of the l a t t e r s t r u c t u r e s t i l l remain. 4 +
4 +
Table V I .
3 +
E s t i m a t e d Values of Energy L e v e l Parameters f o r P a r a m e t r i c M o d e l , i n cm" .
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1
F2 f
44900 36900 25770 1938
F
ζ
Increase
Pu^
3 +
Np
+22% +12% +20% +21%
55000 41300 30800 2350
The e l e c t r o s t a t i c and s p i n - o r b i t p a r a m e t e r s f o r Pu+ which we have d e d u c e d a r e s i m i l a r t o t h o s e p r o p o s e d by Conway some years ago (32). However, i n c l u s i o n of the crystal-field i n t e r a c t i o n i n the computation of the energy l e v e l s t r u c t u r e , w h i c h was n o t done e a r l i e r , s i g n i f i c a n t l y m o d i f i e s p r e v i o u s predictions. As an a p p r o x i m a t i o n , we have c h o s e n t o use t h e c r y s t a l - f i e l d parameters d e r i v e d f o r CS2UCI6 ( 3 3 ) , Table V I I , which together with the f r e e - i o n parameters lead to the p r e d i c t i o n o f a d i s t i n c t g r o u p o f l e v e l s n e a r 1100 cm" . Of course a weaker f i e l d would lead to c r y s t a l - f i e l d levels intermediate between 0 and 1000 cm" . Similar model c a l c u l a t i o n s have been i n d i c a t e d i n F i g . 8 f o r N p ^ , Pu**"*" and Am ** compared t o t h e s o l u t i o n s p e c t r a o f t h e i o n s . F o r Am*"" t h e r e f e r e n c e i s Am ** i n 15 M NHi+F s o l u t i o n ( 3 4 ) . 1
1
+
1
1
1
Table V I I . C r y s t a l - F i e l d Parameters f o r Hexahalide 5 f ^ A c t i n i d e Ions.
2
a
Cs UCl6(5f )
l
CsUF (5f )
2
1
B^
7200 cm
B|>
1300 cm"
h
6
22500 cm
1
6
1
3500 cm"
44550 cm 1
C r y s t a l - f i e l d parameters a r e from Reference w i t h those f o r P a : C s Z r C l ( 5 f ) (43). 1 + +
l
NpF (5f )
8000
cm"
1
33, c o n s i s t a n t
1
2
1
6
^ R e f e r e n c e 40. P r e s e n t work. c
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
c
1
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192
PLUTONIUM CHEMISTRY
I I II
30
28
26
24
22
20
18
16 14 cm" χ I0 1
I
12
I! Ill
I I I II
10
8
I
6
I I I
4
2
3
F i g u r e 8. S o l u t i o n a b s o r p t i o n s p e c t r a f o r N p , P u ^ , and Am^ i n the range 0-30000 cm" w i t h p r e d i c t e d energy level structure indicated. 4 +
+
1
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
+
0
12.
BLAISE ET AL.
Measurement and
Interpretation of Pu
Spectra
It s h o u l d be emphasized t h a t whereas the theoretical m o d e l l i n g of A n s p e c t r a i n t h e c o n d e n s e d phase has r e a c h e d a high degree of sophistication, the type of m o d e l l i n g of e l e c t r o n i c s t r u c t u r e o f t h e ( I V ) and h i g h e r - v a l e n t a c t i n i d e s d i s c u s s e d h e r e i s r e s t r i c t e d t o v e r y b a s i c i n t e r a c t i o n s and i s i n an i n i t i a l s t a t e o f d e v e l o p m e n t . The use o f i n d e p e n d e n t e x p e r i m e n t a l methods f o r e s t a b l i s h i n g t h e symmetry c h a r a c t e r o f observed transitions i s essential to further theoretical i n t e r p r e t a t i o n j u s t as i t was i n t h e t r i v a l e n t i o n c a s e . F o r v a l e n c e s t a t e s h i g h e r t h a n ( I V ) , two t y p e s o f Pu compounds a r e known: t h e s i m p l e and complex h a l i d e s , s u c h as PuF6 and C s P u F 6 , and t h e p l u t o n y l s p e c i e s , P u 0 2 o r Pu02~ ~» The o x y g e n a t e d s p e c i e s a r e e n c o u n t e r e d i n aqueous solutions· However, definitive analyses of the latter type spectra including that characteristic of P u ( V I I ) have yet to be proposed. The d i f f i c u l t y i n a n a l y z i n g t h e s p e c t r a o f p l u t o n y l compounds ( 3 5 ) , i s n o t u n i q u e ; some d e g r e e o f c o n t r o v e r s y s t i l l surrounds the i n t e r p r e t a t i o n of the s p e c t r a of U 0 2 (36). In t h e s p i r i t o f t h e p r e s e n t p a p e r , o u r i n t e r e s t s were t o e x p l o r e some o f t h e c o n s e q u e n c e s o f a p r e d i c t i v e model f o r e n e r g y l e v e l structures. A t p r e s e n t s u c h model c a l c u l a t i o n s a r e b e s t s u i t e d f o r the s p e c t r a of the h a l i d e s . Spectroscopic a n a l y s i s of P u and P u halides i s i n i t s i n i t i a l s t a g e s . No l o w - t e m p e r a t u r e s i n g l e - c r y s t a l s p e c t r a h a v e been r e p o r t e d . A 25°C m u l l s p e c t r u m o f t h e compound Rb2PuF7 was d e s c r i b e d e a r l i e r ( 3 7 ) , and i s now supplemented by t h e results f o r CsPuF6 ( 3 1 ) ; PuFç g a s - p h a s e s p e c t r a have been r e p o r t e d by s e v e r a l d i f f e r e n t g r o u p s a t ANL ( 3 8 - 3 9 ) . One of the methods of estimating the energy level parameters f o r P u i n compounds s u c h as C s P u F c i s t o e x a m i n e t h e m a g n i t u d e o f t h e f r e e - i o n and c r y s t a l - f i e l d p a r a m e t e r s i n other s i m i l a r A n compounds. A l t h o u g h t h e r e are problems w i t h some o f t h e a s s u m p t i o n s t h a t h a v e b e e n made i n a n a l y z i n g t h e s p e c t r a o f compounds s u c h as C s U F e O f ) ( 4 0 - 4 1 ) and C s N p F 6 ( 5 f ) ( 4 2 ) , we t e n t a t i v e l y conclude that the approximate crystal f i e l d p a r a m e t e r s f o r CsUF6 r e p r e s e n t a r e a s o n a b l e s t e p i n t h e p r o g r e s s i o n of 5 f * parameters i n d i c a t e d i n Table V I I . The a c t u a l c r y s t a l f i e l d i n CsPuF6 may be s m a l l e r t h a n i n CsUF6, and c o n s i s t e n t w i t h r e s u l t s r e p o r t e d f o r CsNpFg. I t may a l s o be o f l o w e r symmetry. We c h o o s e h e r e t o use what we b e l i e v e t o be a l i m i t i n g c a s e f o r i l l u s t r a t i o n . The a s s u m p t i o n o f a l a r g e c r y s t a l - f i e l d i n t e r a c t i o n f o r Pu s p e c t r a makes i t n e c e s s a r y t o c o n c l u d e t h a t w h i l e c e r t a i n aspects of e a r l i e r f r e e - i o n e s t i m a t e s (37) are v a l i d , the " a s s i g n m e n t " o f f r e e - i o n s t a t e s t o o b s e r v e d a b s o r p t i o n bands was p r e m a t u r e . Much o f t h e s t r u c t u r e must be due t o c r y s t a l f i e l d components o f many f r e e - i o n g r o u p s t h a t o v e r l a p i n e n e r g y or to v i b r o n i c satellites similar to those encountered i n CS2UCI6 (33). Thus, w h i l e the p r e s e n t computations would agree with earlier work i n interpreting the l e v e l s observed i n
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3 +
+
H
2 +
5 +
6 +
5 +
5 +
1
5 +
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
2
193
194
PLUTONIUM CHEMISTRY
RD2P11F7
as w e l l as i n C s P u F 6 i n t h e r a n g e 6000-7000 cm" as b e l o n g i n g t o a somewhat i s o l a t e d f i r s t e x c i t e d s t a t e , a more d e t a i l e d c a l c u l a t i o n i n c l u d i n g the CsUF6 c r y s t a l - f i e l d gives the results shown i n F i g . 9. I t p r e d i c t s an essentially c o n t i n u o u s l e v e l s t r u c t u r e a t e n e r g i e s >8800 cm" . Extensive d e t a i l e d a n a l y s i s w i l l be r e q u i r e d b e f o r e f i r m a s s i g n m e n t s can be made. However, i t s h o u l d be somewhat more s t r a i g h t - f o r w a r d to u n i q u e l y e s t a b l i s h t h e c r y s t a l f i e l d s p l i t t i n g of the g r o u n d s t a t e by o b s e r v a t i o n o f f l u o r e s c e n c e f r o m t h e f i r s t e x c i t e d s t a t e (-7000 c m " ) . F i n a l l y , the h i g h e s t valence s t a t e r e p o r t e d f o r plutonium i n a n o n - o x y g e n - c o n t a i n i n g compound i s e x e m p l i f i e d i n P u F 6 , whose o p t i c a l s p e c t r u m has been shown t o be e x t r e m e l y complex (39). E s t i m a t e d f r e e - i o n , T a b l e V, and l i g a n d - f i e l d p a r a m e t e r s used i n the present a n a l y s i s are c o n s i s t e n t w i t h those r e p o r t e d earlier (44), but differ considerably from the free-ion p a r a m e t e r s d e v e l o p e d by B o r i n g and Hecht (45) whose v a l u e s f o r F * and F w o u l d a p p e a r t o us t o be d i s t o r t e d . The crystalfield parameters c h a r a c t e r i s t i c of N p F 6 , Table V I I , should r e p r e s e n t a good b a s i s f o r e s t i m a t i n g t h e s i m i l a r i n t e r a c t i o n in PuF6. Our r e s u l t s a r e summarized i n F i g . 10. 1
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1
1
4
6
Recent
observations
of
fluorescence
in
NpF6
and
PuF6
(46)
a r e c o n s i s t e n t w i t h t h e e n e r g y - l e v e l scheme p r o p o s e d . However, comparison of the calculated level structure with highr e s o l u t i o n s p e c t r a o f P u F 6 (44) c o n f i r m s t h a t much o f the observed structure is vibronic in character, built on e l e c t r o n i c t r a n s i t i o n s t h a t a r e f o r b i d d e n by t h e i n v e r s i o n symmetry a t t h e Pu s i t e . Conclusion The i n v e s t i g a t i o n o f Pu f r e e - i o n s p e c t r a has r e a c h e d a p o i n t a t w h i c h f u r t h e r p r o g r e s s i s s l o w b e c a u s e of t h e t i m e c o n s u m i n g a n a l y s i s r e q u i r e d and i n c o m p l e t e n e s s o f the d a t a . In one s e n s e t h e f i r s t phase o f t h i s work i s c o m p l e t e and r e s t s on the existing extensive experimental data base (_3) · The possibilities now exist f o r t a k i n g much h i g h e r r e s o l u t i o n spectra using Fourier-transform methods, but the earlier spectra obtained photographically using high dispersion spectrographs will continue to be an essential building block. The c o m p l e x i t y o f the i n t e r p r e t i v e p r o b l e m , g i v e n t h e many interacting configurations, insures that challenging problems in theory as well as experiment remain to be addressed. I t i s a l s o a p p a r e n t t h a t t h e r e r e m a i n s much t o be done i n developing our u n d e r s t a n d i n g o f the model i n t e r a c t i o n s t h a t b e s t c h a r a c t e r i z e t h e s p e c t r a o f h i g h e r - v a l e n t Pu compounds and indeed of the a c t i n i d e s i n g e n e r a l . The s y n t h e s i s of new compounds w i t h a v a r i e t y o f d i f f e r e n t s i t e s y m m e t r i e s c o u l d be o f p a r t i c u l a r v a l u e i n d e v e l o p i n g more d e t a i l e d c r y s t a l - f i e l d
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
6
6
6
F i g u r e 9. P r e d i c t e d e n e r g y - l e v e l s t r u c t u r e f o r C s U f , C s N p F , and C s P u F i n t h e r a n g e 0-20000 cm-1.
F i g u r e 10. P r e d i c t e d e n e r g y - l e v e l s t r u c t u r e f o r NpFfc, PuFfc, and AmF£ i n t h e r a n g e 0-18000 cm .
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Η-*
3
"Ό S
1'
Β*
•3
ï
3
S
Co
&
>
w Η
C/3 W
•Η
w >
196
PLUTONIUM CHEMISTRY
models. Of equal importance with the theoretical tools is the acquisition of high-resolution spectra under conditions that permit the independent experimental definition of properties that will help characterize the observed transitions. It is the lack of a solid experimental basis that has inhibited more widespread interest in the theoretical modelling.
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Literature Cited 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.
Fred, M. Adv. Chem. Ser. 1967, 71, 180-202. Blaise, J.; Fred, M.; Gutmacher, R. J. Opt. Soc. Am. (to be submitted). Fred, M.; Blaise, J. Argonne National Laboratory Report, 1983, in preparation. Conway, J. G.; Blaise, J.; Verges, J. Spectrochimica Acta 1976, 31B, 31-47; Conway, J. G. "Handbook of Chemistry and Physics", Weast, R. C.; Astle, M. J., Eds. CRC Press, Boca Raton, 1980, pp. E-290-1. Striganov, A. R., Report IAE-2965, Kurchatov Institute of Atomic Energy, Moscow, 1978 (in Russian). Translated by G. V. Shalimoff, Lawrence Berkeley Laboratory. Carnall, W. T. "Gmelin Handbook of Inorganic Chemistry", Transurane A-2 (Erg.-Werk Band 8) Verlag Chemie, Weinheim/Bergstr., 1973, 35-79. Rollefson, G. K.; Dodgen, H. W. "Report on Spectrographic Analysis Work CK-812", July 1943 (Declassified 29 December 1954). McNally Jr., J. R.; Griffin, P. M. J. Opt. Soc. Am. 1959, 49, 162-6. Bovey, L.; Gerstenkorn, S. J. Opt. Soc. Am. 1961, 51, 522-5. Bovey, L.; Ridgeley, A. "The Zeeman Effect of Pu I", A.E.R.E.-R3393, Harwell, 1960. Gerstenkorn, S. Ann Physique (Paris) 1962, 7, 367-404. Striganov, A. R.; Korostyleva, L. Α.; Dontsov, Yu, P. Zh. Eksp. Teor. Fiz. 1955, 28, 480; Sov. Phys. JETP 1955, 1, 354. Korostyleva, L. A. Opt. i. Spektroskopiya 1963, 14, 177; Opt. Spectrosc. (USSR) 1963, 14, 93. Korostyleva, L. Α.; Striganov, A. R. Opt. i . Spectroskopiya 1966, 20, 545-53; Opt. Spectrosc. (USSR) 1966, 20, 309-17. Blaise, J.; Fred, M.; Gerstenkorn, S.; Tomkins, F. S. 2nd E.G.A.S. Conference, Hanover, 14-17 July 1970. Blaise, J.; Steudel, A. Z. Physik 1968, 209, 311-28. Wilson, M. Phys. Rev. 1968, 176, 58-63. Rajnak, K.; Fred, M. J. Opt. Soc. Am. 1977, 67, 1314-23. Brewer, L. J. Opt. Soc. Am. 1971, 61, 1101-11, 1666-82. Blaise, J.; Fred, M.; Gerstenkorn, S.; Judd, B. R. C. R. Acad. Sci. Paris 1962, 255, 2403-5.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
12. 21. 22. 23.
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24. 25.
26. 27. 28.
29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42.
BLAISE ET AL.
Measurement and Interpretation of Pu Spectra
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