5p-3d AND 4f-3d EMISSIONS IN La, Ba AND Cs HALIDES

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5p-3d AND 4f-3d EMISSIONS IN La, Ba AND Cs HALIDES

P. Martin, E. Belin, A. Maquet, C. Bonnelle

To cite this version:

P. Martin, E. Belin, A. Maquet, C. Bonnelle. 5p-3d AND 4f-3d EMISSIONS IN La, Ba AND Cs HALIDES. Journal de Physique Colloques, 1987, 48 (C9), pp.C8-649-C8-652.

�10.1051/jphyscol:19879111�. �jpa-00227219�

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JOURNAL DE PHYSIQUE

Colloque

C9,

supplement au n012, Tome 48, decembre 1987

5p-3d AND 4f-3d EMISSIONS IN La,Ba AND Cs HALIDES

P. MARTIN, E. BELIN, A. MAQUET and C. BONNELLE

Laboratoire de Chimie Physique, Universite Pierre et Marie Curie, 11, Rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France

Rdsumd: Le code MCDF de Grant a dtd u t i l i s d pour c a l c u l e r l e s d n e r g i e s d e s Bmissions 5p-3d e t 4f-3d dues 1 l a r e o r g a n i s a t i o n d ' d t a t s 3d94f1 dans ~ a ~ + , ~ a e t ~CS+ + a i n s i que l e s dmissions 5p-3d a s s o c i d e s

P

l a c o n f i g u r a t i o n 3d9. Les r d s u l t a t s explrimen- t a u x e t t h l o r i q u e s s o n t en bon accord 1 l ' e x c e p t i o n de l ' d m i s s i o n 4f-3d dans l ' d t a t e x c i t d cs+3d94f1. De p l u s , l l i n t e n s i t d des r a i e s 5p-3d e t 3d-4f s ' i n v e r s e l e long de l a s b r i e . Ces e f f e t s s o n t expliquds par l ' e x t e n s i o n des o r b i t a l e s 4f. P a r a i l l e u r s , une i n t e r p r e t a t i o n des s p e c t r e s de p h o t o e l e c t r o n s 3d e s t propos6e.

A b s t r a c t :

rant's

MCDF code has been used t o c a l c u l a t e t h e e n e r g i e s o t h e 5 -3d and Of-3d emissions due t o t h e r e o r g a n i s a t i o n of t h e 3d9hf l s t a t e s i n La5', Ba2' and CS' and a l s o t h e 5p-3d emissions a s s o c i a t e d t o t h e 3d9 c o n f i g u r a t i o n . Good agreement i s found between our experimental and c a l c u l a t e d d a t a w i t h e x c e p t i o n f o r t h e 4f-3d emis- s i o n s from CS+ 3d94f1 e x c i t e d s t a t e . This d i s c r e p a n c y and t h e i n v e r s i o n of 5p-3d and 4f-3d emission i n t e n s i t i e s along t h e s e r i e s a r e explained i n terms of t h e 4f

o r b i t a l s p a t i a l e x t e n s i o n . I n t e r p r e t a t i o n i s a l s o given f o r t h e 3d p h o t o e l e c t r o n s p e c t r a .

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I n a previous paper ( I ) , we had suggested t h a t i n LaF3 3d 4f s t a t e s a r e c r e a t e d by d i r e c t c o l l i s i o n a l e x c i t a t i o n and c a n be regarded a s q u a s i atomic-like s t a t e s i n t h e s o l i d without s i g n i f i c a n t i n t e r a c t i o n w i t h t h e underlying continua. We had a t t r i b u t e d t h e most i n t e n s e La emissions i n t h i s compound t o r a d i a t i v e recombina- t i o n of t h e s e s t a t e s towards e i t h e r t h e 3d1° ground s t a t e ( r e s o n a n t emission) o r

5 1

5p 4f s t a t e s (5p-3d emissions i n t h e presence of a 4f s p e c t a t o r e l e c t r o n ) .

To v e r i f y t h i s i n t e r p r e t a t i o n , we have c a l c u l a t e d t h e e n e r g i e s of t h e reson- a n t emissions and t h a t of 5p-3d t r a n s i t i o n s i n t h e e x c i t e d and i o n i z e d systems. These v a l u e s a r e compared t o experimental e n e r g i e s and t o d a t a obtained from l e v e l e n e r g i e s a s deduced from p h o t o e l e c t r o n spectroscopy.

Both c a l c u l a t i o n s and experiments have been extended t o BaF2 and CsCl com- 9 1

pounds where 3d 4f e x c i t e d s t a t e s can a l s o be c r e a t e d by d i r e c t e x c i t a t i o n .

G r a n t ' s MCDF code has been used t o g e n e r a t e t h e t r a n s i t i o n e n e r g i e s i n r e l e - vant c o n f i g u r a t i o n s from t h e La, Ba and Cs Xe-like systems i n t h e ground s t a t e . For La, t h e r a d i a l c o r r e l a t i o n s between 3d and 4d s u b s h e l l s have been considered and in- cluded i n t h e c a l c u l a t i o n s .

Table 1 summarizes t h e d a t a f o r LaF from both t h e o r e t i c a l c a l c u l a t i o n s and 3

experiments ( c f . f i g . 1 ) . X-ray emissions a r e induced by i r r a d i a t i n g t h e samples by e l e c t r o n s w i t h energy about 1.9 times t h e 3d l e v e l t h r e s h o l d energy. A very good

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879111

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C9-650 JOURNAL DE PHYSIQUE

agreement is found between the energies calculated and measured for the emissions from the 3d-,„4f excited state ( lines 1,3 and 5 ) . The same agreement exists for the 3d„ ,„4f excited state. On the other hand, the energy of the 5p-3d,-,„ emission in the ion (line 2) agrees with data deduced from energy level tables.

These results confirm our previous interpretations.

They allow also to interpret the two peaks observed in the La 3d„ ,_ XPS spectrum whose res- pective binding energies are:

837.7 eV and 841.6 eV (2).

From these two values and frran the energy of the 5p level i.e.

18.8 eV, the 5p-3d,-,„ emission line in the ion is predicted to be either at 818.9 eV or 822.8eV.

Comparison with our experimental value i.e. 817.2 eV , shows that

the lower binding energy peak 9

(837.7 eV) corresponds to the final state of 3d configuration. Then, the 3d./? peak of higher binding energy corresponds to a doubly excited-ionized final state obtained by shake-up process. Indeed in LaF_, the 4f level being located close to the middle of the band gap in the presence of the 3d inner hole (1), the energy of the shake-up process from the ligand valence band to 4f is of the order of 4 eV. Consequently, the photoelectron peak of 841.6 eV can be interpreted as a transition to the 3d,. . L 4f configuration state. Such a state can be created by electron irradiation? it can decay radiatively with emission of a resonance line satellite: 3d,-/pL 4f —>• L . W e sug- gest line 6 can be identified to this satellite.

Fig 1: 5p-3d and 4f-3d emissions in LaF.,

1 2

3 4 5

6

X - r a y t r a n s i t i o n

5 p "14 f1 3 d j J24 fa

5 p_ 1 3 d "1

Sp'^-tf¹ S d j ^ f¹

3 d5 / 24 f 2 4 f l

3 d5 / 24 f l

fundamental - 1 - 1 1 - 1 3d % 4 f L

e x p e r i m e n t

• 0.2 eV 8 1 2 . 2 eV

8 1 7 . 2 eV 8 2 7 . 1 eV

8 3 1 . 8 eV

# 3 4 . 8 eV

8 3 7 . 9 eV

c a l c u l s e x c i t a t . 8 1 2 . 2 eV

8 2 7 . 0 eV

8 3 4 . 9 eV t i o n i o n i s a t .

8 2 0 . 8 eV

f r o m e n e r g y l e v e l s

8 1 7 . 3 eV

LaF - Table I

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C9-651

On the other hand, characteristic isochromat spectroscopy allowed us to 9 2

interpret line 4 as a resonant emission from the 3d 4f negative ion created by at- tachment of an incident electron (1).

Figure 2 shows the 5p-3d and 4f-3d emission spectra obtained for BaF„: the resonant lines are still the most intense ( lines 5) but the 5p-3d emissions in the excited state (line 1) are now negligible with respect to the emissions in the ion (lines 2 ) . As for LaF,, the agreement between experimental and calculated energies is good for the transitions from the excited states.

The transition energies in the ion agree well with the values deduced from tabulated energy levels

(cf.table 2 ) . The lines labelled (6) and (6') are attributed to

9 -1 I satellites of resonant lines from states of configuration 3d L 4f .

fig 2 : 5p-3d and 4f-3d emissions in BaF„

2 1 2 2 5

5 X-ray t r a n s i t i o n

5 p3 / 2 " *3 d5 / 2

5P i / 24 f^3 d3 / 24 f l 5P l / 2 - *3 d3 / 2

5P>3/2-»3d3/2

3 d5 / 24 f l — fundamental 3 di/2«1-^

experiment + 0.2 eV 766.3 eV 771.5 eV

779.6 eV 781.6 eV 785.3 eV

800.1 eV

B calcul i o n i s a t .

763.4 eV

776.7 eV 778.8 eV

a t i o n e x c i t a t .

771.0 eV

784.8 eV

789.8 eV

1 from energy l e v e l s

766.1 eV

779.5 eV 781.5 eV

experiment + 0.3 eV

713.4 e\l

725.7 eV 727.4 eV 734.0 eV

748.0 eV

CsCl calculal 1 l o n i s a t .

711.0 eV

723.5 eV -ion

e x c i t a t .

726.9 eV

740.9 eV

1 from ener- 'gy l e v e l s 714.1 eV

726.4 eV 728.1 eV

Table II

For CsCl, an inversion of the relative intensities of the 5p-3d lines as compared to the 4f-3d is observed and only the 5p-3d transitions in the ion are pre- sent (Fig.3). Moreover, the 4f-3d resonant lines are asymetrical in shape and their calculated energies are 7 eV lower than experimental values (Table 2 ) . This behavior can be ascribed to the very large spatial extension of 4f orbitals in Cs with respect to La and Ba. ( Fig.4). Indeed, the nature of the 3d 4f excited states differ along 9 1

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JOURNAL

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t h e La-Cs s e r i e s . For CsC1, t h e p o t e n t i a l b a r r i e r c r e a t e d by t h e ~ 1 - i o n s surrounding each CS+ t r a p s t h e e x c i t e d e l e c t r o n on t h e atom w i t h t h e c o r e h o l e ( 3 ) . Analogy e x i s t s between t h i s type of e x c i t e d s t a t e s and those observed f o r N i small p a r t i c l e s (4). I n c o n t r a s t , i n ~ aand ~ a ~ + , ~ + t h e e x c i t e d s t a t e s a r e e n t i r e l y i n t e r p r e t e d by t h e very s t r o n g l o c a l i z a t i o n of t h e 4f o r b i t a l s on t h e c o r e of t h e atom.

.d

H 0

I 2

710 730 750

Energy i n eV

F i g 3: 5p-3d and 4f-3d emissions i n C s C l

r ( a o )

F i g 4: 4fgi2 wave f u n c t i o n s

I n summary, i n t h e t h r e e c a s e s considered here, t h e e x c i t e d s t a t e s a r e created by d i r e c t c o l l i s i o n a l i n t e r a c t i o n between t h e i n c i d e n t e l e c t r o n s and t h e 3d sub- s h e l l . These r e s u l t s show t h a t t h e e l e c t r o e x c i t a t i o n c r o s s - s e c t i o n s a r e s t i l l n o t i - c e a b l e a t about two times t h e 3d t h r e s h o l d energy.

REFERENCES

1- P.MOTAIS, E.BELIN, C.BONNELLE- Phys. Rev. B 30 n06, 4399 (1984) 2-H.BERTHOU- ThPse. P a r i s 1976

3-P.MOTAIS,E.BELIN,C.BONNELLE- Phys. Rev. B 25 n08, 5492 (1982) 4-F.VERGAND,D.FARGUES,C.BONNELLE- This conference

5-P.MARTIN- Unpublished

ACKNOWLEDGMENTS: The L a b o r a t o i r e de Chimie Physique i s an U n i t 6 Associde au CNRS, UA 176. The numerical computations r e p o r t e d h e r e have been performed a t t h e CIRCE c e n t e r .