Measurement and Interpretation of Plutonium ... - ACS Publications

12 Measurement and Interpretation of Plutonium Spectra

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on October 6, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch012

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.


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


BLAISE ET AL.

Measurement and Interpretation of Pu Spectra


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


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


2 i + 0

2

2



BLAISE ET AL.


—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



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



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 .


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


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



BLAISE ET AL.

181

AnIf "'d


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 .


Ν

PLUTONIUM CHEMISTRY

182

An H f

Ν

An llf

(lO^m-'l

N-l

(I0 cn 3


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.


L II Es

Ν


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



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 +


12.

BLAISE ET AL.

Table I I I ( A ). Spectrum


HFR

a

Values for 5 f

Configuration

I

5 f 7s 5

5f 6d7s

2


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).


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.


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


6

12.

BLAISE ET AL.


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 .


187


PLUTONIUM CHEMISTRY


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


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


189


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


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" .


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


c

1


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


+

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


3 +

+

H

2 +

5 +

6 +

5 +

5 +

1

5 +


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


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



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 .


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.


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.


12. 21. 22. 23.


24. 25.

26. 27. 28.

29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42.

BLAISE ET AL.


Bauche, J.; Blaise, J.; Fred, M. C. R. Acad. Sci. Paris 1963, 256, 5091-93; 257, 2260-63. Blaise, J.; Wyart, J. F.; Conway, J. G.; Worden, E. F. Physica Scripta 1980, 22, 224-30. Bauche-Arnoult, C.; Gerstenkorn, S.; Verges, J.; Tomkins, F. S. J. Opt. Soc. Am. 1973, 63, 1199-1203. Cowan, R. D.; Griffin, C. D. J. Opt. Soc. Am. 1976, 66, 1010-14. Crosswhite, H. M. Colloques Internationaux du C.N.R.S., Spectroscopie des Elements de Transition et des Elements Lourds das les Solids, 28 Juin - 3 Juillet 1976, Editions du C.N.R.S., Paris 1977, 65-69. Edelstein, N.; Easley, W.; McLaughlin, R. Adv. Chem. Ser. 1967, 71, 203-10. Peterson, J. R.; Fellows, R. L.; Young, J. P.; Haire, R. G. Radiochem. Radioanal. Letters 1977, 31, 277-82. Fellows, R. L.; Peterson, J. R.; Young, J. P.; Haire, R. G. "The Rare Earths in Modern Science and Technology", McCarthy, G. J.; Rhyne, J. J., Eds. Plenum Corp., New York 1978, 493-99. Conway, J. G.; Rajnak K. J. Chem. Phys. 1966, 44, 348-54; Hessler, J. P.; Carnall, W. T. ACS Sympos. Ser. 1980, 131, 349-68. Carnall, W. T.; Fields, P. R.; Pappalardo, R. G. J. Chem. Phys. 1970, 53, 2922-38. Morss, L. R.; Williams, C. W.; Carnall, W. T. Chapter in this book. Conway, J. G. J. Chem. Phys. 1964, 41, 904-5. Johnston, D. R.; Satten, R. Α.; Schreiber, C. L.; Wong, Ε. Y. J. Chem. Phys. 1966, 44, 3141-3. Asprey, L. B.; Penneman, R. A. Inorg. Chem. 1962, 1, 134-36. Einstein, J. C.; Pryce, M. H. L. Proc. Roy. Soc. 1956, A238, 31-45; J. Res. Natl. Bureau Stds. 1966, 70A, 165-73. Carnall, W. T. "Gmelin Handbook of Inorganic Chemistry", 8th Ed., System 55, Springer-Verlag, Berlin, 1982, 147-57. Varga, L. P.; Reisfeld, M. J.; Asprey, L. B. J. Chem. Phys. 1970, 53, 250-55. Weinstock, B.; Malm, J. G. J. Inorg. Nucl. Chem. 1956, 2, 380-94. Steindler, M. J.; Gunther, W. H. Spectrochim. Acta 1964, 20, 1319-22. Reisfeld, M. J.; Crosby, G. A. Inorg. Chem. 1965, 4, 65-70. Leung, A. F. J. Phys. Chem. Solids 1977, 38, 529-32. Hecht, H. G.; Varga, L. P.; Lewis, W. B.; Boring, A. M. J. Chem. Phys. 1979, 70, 101-108; Poon, Y. M.; Newman, D. J. J. Chem. Phys. 1982, 77, 1077-79.


197

198 43. 44.


45. 46.

PLUTONIUM CHEMISTRY

Axe, J. D. "Electronic Structure of Octahedrally Coordinated Protactinium(IV) in Cs 2 ZrCl 6 ", UCRL-9293, Berkeley, 1960. Kugel, R.; Williams, C.; Fred, M.; Malm, J. G.; Carnall, W. T.; Hindman, J. C.; Childs, W. J; Goodman, L. S. J. Chem. Phys. 1976, 65, 3486-92. Boring, M.; Hecht, H. G. J. Chem. Phys. 1978, 69, 112-16. Beitz, J. V.; Williams, C. W.; Carnall, W. T., Chapter in this book.

RECEIVED

January 7,1983


Measurement and Interpretation of Plutonium ... - ACS Publications

Recommend Documents