HIGH-RESOLUTION AUGER SPECTRA OF Li, Be, B AND C EXCITED IN SINGLE GAS COLLISIONS

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HIGH-RESOLUTION AUGER SPECTRA OF Li, Be, B AND C EXCITED IN SINGLE GAS COLLISIONS

P. Bisgaard, R. Bruch, M. Rødbro

To cite this version:

P. Bisgaard, R. Bruch, M. Rødbro. HIGH-RESOLUTION AUGER SPECTRA OF Li, Be, B AND C

EXCITED IN SINGLE GAS COLLISIONS. Journal de Physique Colloques, 1979, 40 (C1), pp.C1-14-

C1-16. �10.1051/jphyscol:1979104�. �jpa-00218383�

JOURNAL DE PHYSIQUE Colloque C1, supplkment au n

"

HIGH-RESOLUTION AUGER SPECTRA OF L i , Be, B AND C EXCITED I N SINGLE GAS COLLISIONS

P. Bisgaard, R. Bruch ') and M. Rbdbro

I n s t i t u t e o f Physics, U n i v e r s i t y o f Aarhus, DK-8000 Aarhus C, Denmark +) F a k u l t X t fir Physik, U n i v e r s i t d t Freiburg, D - 7800 Freiburg, West Germany

Ri?sum@. Nous avons 6 t u d i e des spectres Auger a' haute r e s o l u t i o n du l i t h i u m , b e r y l l i u m ,

bore

A b s t r a c t . We have s t u d i e d h i g h - r e s o l u t i o n Auger spectra o f l i t h i u m , b e r y l l i u m , boron and carbon e x c i t e d i n s i n g l e gas c o l l i s i o n s .

Despite t h e fundamental importance o f e l e c t r o n c o r r e l a t i o n i n h i g h l y e x c i t e d atoms and ions [I], very few d a t a e x i s t f o r s i n g l y - and doubly c o r e - e x c i t e d s t a t e s i s o e l e c t r o n i c w i t h He and L i . T h i s work i s concerned w i t h t h e experimen- t a l study o f p r o j e c t i l e - A u g e r e l e c t r o n emission from f a s t moving L i , Be, B and C i o n beams, which were passed through t h i n gas t a r g e t s . F o r t h e f i r s t t i m e we g i v e a d e t a i l e d a n a l y s i s o f t h e Auger-electron s p e c t r a f o r t h e low-Z elements. I n p a r t i c u l a r we have s t u d i e d i s o e l e c t r o n i c sequen- ces o f t h e most prominent s i n g l y c o r e - e x c i t e d li- t h i u m - l i k e and doubly c o r e - e x c i t e d h e l i u m - l i k e s t a t e s [ 2 ] . Furthermore, we have e x t r a c t e d f r e e - atom K - s h e l l b i n d i n g energies f o r Be, B and C from our p r o j e c t i l e - A u g e r s p e c t r a [3].

We have r e c e n t l y demonstrated t h a t h i g h r e s o l u t i o n i s obtained i n p r o j e c t i l e - A u g e r spectroscopy u s i n g s i n g l e - c o l l i s i o n gas e x c i t a t i o n

[ 4

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The L i , Be, B and C i o n beams were s u p p l i e d by t h e 600-keV heavy-ion a c c e l e r a t o r a t t h e U n i v e r s i t y o f Aarhus. E l e c t r o n s e j e c t e d from t h e t a r g e t /region were analyzed by an e l e c t r o - s t a t i c para1 le l - p l a t e spectrometer which can be c o n t i n u o u s l y r o t a t e d between 0' and 150'. A view

o f t h e t a r g e t r e g i o n i s shown i n F i g . 1. For nor- m a l i z i n g purposes, t h e i o n beam was c o l l e c t e d i n Faraday cup 2 f o r small observation angles (see F i g . 1). T y p i c a l target-gas pressures were ^Q, t o r r t o ensure s i n g l e - c o l l i s i o n c o n d i t i o n .

TARGET VACUUM

.. /'-hMu.

ION BEAM

wo 0 ELECTRON

F i g . 1

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The p r o j e c t i l e - A u g e r e l e c t r o n spectra were s t u d i e d f o r i n c i d e n t beam energies o f 100 t o 500 keV e x c i t e d i n s i n g l e c o l l i s i o n s w i t h ato- mic and molecular t a r g e t s such as He, L i , Ne, H2, CH4 and N2. Helium, i n p a r t i c u l a r was selected because o f t h e small p r o j e c t i l e s c a t t e r i n g angle f o r K - s h e l l e x c i t a t i o n g i v i n g small Doppler broa- dening [ 2 ] . I n a d d i t i o n helium i s the s i m p l e s t atomic t a r g e t , which may f a c i l i t a t e an understan- d i n g o f t h e c o l l i s i o n a l processes. On t h e o t h e r hand molecular t a r g e t s scch as CH4 were found t o

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979104

F i g . 2

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c1-16 JOURNAL DE PHYSIQUE

g i v e h i g h e r e x c i t a t i o n p r o b a b i l i t i e s f o r helium- REFERENCES and l i t h i u m - l i k e doubly c o r e - e x c i t e d s t a t e s .

A t y p i c a l h i g h - r e s o l u t i o n Auger spec- trum i s presented i n F i g . 2. The observed s p e c t r a l features as i n d i c a t e d i n F i g . 2 can be associated w i t h doubly c o r e - e x c i t e d s t a t e s i n L i I and L i I I .

Whenever t h e r e i s more than one s e r i e s f o r a given S, L and n, t h e mixings between t h e d i f f e r e n t c o n f i g u r a t i o n s are so g r e a t t h a t c l a s - s i f i c a t i o n s based on s i n g l e products o f o r b i t a l s are n o t v a l i d . For H e - l i k e s t a t e s we use t h e no- t a t i o n (N,na)(2S + I ) , L, n, where N i s t h e i n n e r - e l e c t r o n quantum number, n i s t h e o u t e r - e l e c t r o n r a d i a l quantum number and a = a, b, c,

. . ..

The lowest p o s s i b l e Auger decay i n

1 1

L i I I i s (2,2a) S -+ ( 1 % ~ ) S. T h i s l i n e i s observ- ed a t 70.65 eV (peak 18). Peak 19 (see F i g . 2)

3 o

o r i g i n a t e s from t h e (2,2a) P s t a t e i n L i I I . Fur- thermore, peak 20 can be associated w i t h t h e (2,2a) D l e v e l . There might be a s u p e r p o s i t i o n 1 o f two l i n e s i n t h e r e g i o n o f peak 21, namely t h e (2,2a)'p0 + ( 1 s ~ ~ ) ' ~ ~ and i h e ( 2 ~ ~ 2 ~ ) ~ ~ " l l s p ( 'PO)ES decays.

A u t o i o n i z a t i o n l i n e s observed between 78.13 and 83.36 eV (see F i g . 2) a r e expected t o a r i s e from doubly core-excited s t a t e s i n L i I . An- o t h e r s u r p r i s i n g f e a t u r e i s t h e s t r o n g p o p u l a t i o n of 2131' h i g h angular momentum s t a t e s such as

1 3

( 2 , 3 a 1 3 ~ and D, ( z , ~ ~ ) ~ F o and 'FO and (2,3b) D and D. 1

To conclude, Auger t r a n s i t i o n ener- g i e s f o r many p r e v i o u s l y unknown s t a t e s i n L i , Be, B and ; have been measured u s i n g t h e p r o j e c t i l e - Auger-spectroscopy method 1 2 1 . These new d a t a might be o f p a r t i c u l a r importance t o t e s t and im- prove i o n i c wave f u n c t i o n s i n c l u d i n g t h e e f f e c t s of e l e c t r o n c o r r e l a t i o n .

[I]

-

[z]

B: Atom. Molec. Phys. (1978) t o be published.

[ 3 ] P. Bisgaard, R. Bruch, P. Dahl, B. Fastrup and M. Rddbro, Physica S c r i p t a

17,

[4] M. Rddbro, R. Bruch and P. Bisgaard, J. Phys.

B: Atom. Molec. Phys.

10,

[ 5 ] M. Rddbro, R. Bruch, P. Bisgaard, P. Dahl and B. Fastrup, J. Phys. B: Atom. Molec. Phys.

10, L 483 (1977).

-

[ 6 ] R. Bruch, M. Rddbro, P. Bisgaard and P. Dahl ,

Phys. Rev. L e t t .

2,