X-UV SPECTROSCOPY OF LOW ENERGY CHARGE EXCHANGE COLLISIONS

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X-UV SPECTROSCOPY OF LOW ENERGY CHARGE EXCHANGE COLLISIONS

S. Bliman, J. Bonnet, M. Bonnefoy, S. Dousson, Agnès Fleury, D. Hitz, T. Lu Dac, M. Mayo

To cite this version:

S. Bliman, J. Bonnet, M. Bonnefoy, S. Dousson, Agnès Fleury, et al.. X-UV SPECTROSCOPY OF

LOW ENERGY CHARGE EXCHANGE COLLISIONS. Journal de Physique Colloques, 1986, 47

(C6), pp.C6-41-C6-46. �10.1051/jphyscol:1986605�. �jpa-00225848�

X-UV SPECTROSCOPY OF LOW ENERGY CHARGE EXCHANGE COLLISIONS

S. BLIMAN, J.J. BONNET*, M. BONNEFOY*, S. DOUSSON, A. FLEURY', D. HITZ, T. L U DAC and M. MAY0

AGRIPPA, Bat. 10.05, CENG 85X, F-38041 Grenoble Cedex, France ' ~ a b o r a t o i r e d e Physique des Collisions Atomiques, C.N.A.M., 292, Rue Saint-Martin, F-75141 Paris Cedex 0 3 , France

Resum@ : Dans l e domaine de l a physique des plasmas chauds, l a modelisation de 7 1 i b r e d ' i o n i s a t i o n des impuretes suppose l a connaissance de l a r e l a t i o n entre processus coll isionnel s e t rayonnement.

On montre que, considerant l e processus d'echange de charge entre ion fortement charge de f a i b l e v i t e s s e e t atome, on e s t en presence d'une source de rayongell)fnt

Fondamentalement, 2 des v i t e s s e s f a i b l e s ( v q v v i t e s s e atomique unit&

= 2 , 2 10 cm/s), l a capture d'un electron l a i s s e l e proJec?ile dans u n 6 t a t e x c i t e . Le niveau quantique n l e plus probablement peuple depend de l a charge de 1 'ion in- cident e t du potentie!? d'ionisation de 1 'atome c i b l e . Le melange Stark post-colli- sionnel r e d i s t r i b u e l e s populations de n dans l e s sous-@tats 1. Ceci e s t note l o r s de l'observation de l a cascade radiative? Des exemples montrent que, avec des ions de charge i n i t i a l e +8, l a capture sera dominante dans n

5 dans des c o l l i s i o n s sur H2 e t dans n

4 dans des c o l l i s i o n s sur He, Des spectres obtenus avec d i f f e r e n t s ions montrent un nombre important de t r a n s i t i o n s inconnues. Leur i d e n t i f i c a t i o n e s t f a c i l i t e e par l e f a i t que l e rayonnement provient d'un ion de nature determinee e t d'un seul @ t a t de charge. Enfin, quand niveaux d l @ n e r g i e e t longueurs d'onde des t r a n s i t i o n s ainsi que probabilite de t r a n s i t i o n s sont connus, on peut reconstruire l a dynamique de l a c o l l i s i o n e t finalement obtenir l a section e f f i c a c e t o t a l e d ' e - change de charge.

Abstract : In the f i e l d of hot plasmas, i t i s well known t h a t a knowledge of the r e l a t i o n between c o l l i s i o n s and radiation i s needed.

We show t h a t considering the charge exchange process in which a highly charged, low velac-ity ion impinges on an atom, we have an X-UV l i g h t source a l l o - wing new developments.

Basically, a t v e l o c i t i e s l e s s than the atomic u n i t (v

2 . 2 10 cm/s), 8 the capture of one electron will leave the p r o j e c t i l e ion i n an ex?ited s t a t e . The most probably populated level n i s dependant on the p r o j e c t i l e i n i t i a l charge and the t a r g e t ionization p o t e n t i a l ? Post c o l l i s i o n Stark mixing r e d i s t r i b u t e s among substates i n the capture level. This i s reflected in the r a d i a t i v e decay which i s thus observed. Examples show t h a t f ~ r i n i t i a l charge 8+ ions colliding w i t h Hydro- gen capture goes mostly t o n = 5 whereas i n c o l l i s i o n s on Helium capture i s mostly on n = 4. Detailled spectrum obtained w i t h d i f f e r e n t species i n the X-UV range re- veal an enormous number of unknown l i n e s . Their i d e n t i f i c a t i o n i s f a c i l i t a t e d by the f a c t t h a t only one charge s t a t e r a d i a t e s . Finally, when the r a d i a t i v e pattern i s analyzed, a reconstruction of the c o l l i s i o n dynamics i s possible giving the cap- t u r e cross section.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986605

JOURNAL D E PHYSIQUE

INTRODUCTION

Great i n t e r e s t has developped f o r the s t u d i e s of low energy charge exchange c o l - l i s i o n s between h i g h l y charged i o n s and atoms.

n

A t v < vo (atomic u n i t v e l o c i t y = 2.2 x 10' cm/s), i n t h e process

A ~ + + B + A ( ~ - { A ~ + ^B+, the capture i s s t a t e s e l e c t i v e . That i s a l i m i t e d number o f l e v e l ( s ) i s populated; t h e d i s t r i b u t i o n among substates 1 v a r i e s w i t h t h e p r o j e c - t i l e v e l o c i t y and r e f l e c t s the p o s t c o l l i s i o n S t a r k mixing.

THEORETICAL SITUATION

The c o l l i s i o n a l s i t u a t i o n which has been m o s t l y considered i s t h e case o f com- p l e t e l y s t r i p p e d i o n s i n t e r a c t i n g w i t h a hydrogen atom i n i t s ground s t a t e / I / . A 1 im i t e d number o f treatments were centered on f u l l y s t r i p p e d p r o j e c t i l e s i n t e r a c - t i n g w i t h He 121. I n t h e o t h e r cases, an e m p i r i c a l d e s c r i p t i o n o f t h e c o l l i s i o n can be considered. The c o l l i s i o n p a r t n e r s behave quasi hydrogenical l y . The e l e c t r o n ( t r a n s f e r e d from t h e atom t o t h e i o n ) p o t e n t i a l energy i s t h e superposed coulomb a t t r a c t i o n s o f the i o n and atom. Capture occurs i f the e l e c t r o n energy on atom B i s equal t h e e l e c t r o n energy on i o n A; t h i s takes p l a c e a t an i n t e r n u c l e a r d i s t a n c e - ^.-

R < ( 1 + 24'") / IB ( I B i o n i z a t i o n p o t e n t i a l o f B).

The most - probably popu$ated

l e v e l on A w i l l be g i v e n by :

( 1 ) IB i s i n atomic u n i t s /3/

F o r t h e cases considered here a f t e r , i t i s e a s i l y seen t h a t i o n s w i t h i n i t i a l charge Q = 8, c a p t u r i n g from He would populate m o s t l y n = 4 whereas a c o l l i s i o n on H2 would populate n

5. This simple semi-empirical d e s c r i p t i o n gives no i n d i c a t i o n on p o p u l a t i o n s h a r i n g among substates 1.

EXPERIMENTAL RESULTS

D i f f e r e n t s i t u a t i o n s a r e encountered.

1) Simple cases - The data f o r energy l e v e l s , t r a n s i t i o n p r o b a b i l i t i e s and t r a n s i t i o n wavelength a r e known f o r t h e i o n a f t e r e l e c t r o n capture. With these and u t i l i z i n g an i n t e n s i t y c a l i b r a t e d spectrometer, a f u l l r e c o n s t r u c t i o n o f t h e l e v e l and sublevels p o p u l a t i o n i s p o s s i b l e / I / .

a ) Case o f ~ e * + - F i g . l a and b show r e s p e c t i v e l y spectra r e s u l t i n g from cascades upon capture from He and H taken i n t h e same experimental c o n d i t i o n s . A f u l l a n a l y s i s of t h e cascade shows $hat p o p u l a t i o n s a r e n o t shared s t a t i s t i c a l l y among t h e capture l e v e l substates. T h i s i s shown i n f i g . 2a and b. I n these condi- t i o n s , summing up a l l p a r t i a l capture cross s e c t i o n s g i v e s t h e t o t a l capture cross section. T h i s i s shown i n f i g . 3, where i s a l s o drawn t h e cross s e c t i o n deduced from an experimental s c a l i n g law /4/

a = 4 x 1 0 ~ ' ~ an2 (2) where I .P. i s t h e t a r g e t ( 4 4 - 1 IP (eV) i o n i z a t i o n p o t e n t i a l

b) Case o f ~ r * + - With t h e above mentionned estimate o f t h e most probably populated l e v e l , f o r a c o l l i s i o n on He and on H , t h e c a p t u r e should go t o n = 4

(case o f He) and n = 5 (case o f HZ). With a bea$ o f constant i n t e n s i t y ( I .. ^{1.7 d)}

o f w e l l i d e n t i f i e f 2 a n d pure 45 i o n s o f charge t o mass r a t i o 0.2 and t a r g e t thicknes-

ses o f o r d e r 1x10 atoms cm ( s i n g l e c o l l i s i o n c o n d i t i o n ) . The spectra show a

c l e a r capture t o n

4 (case o f He) and n = 5 (case o f Hz). T h i s i s seen i n t h e

spectra obtained a t a c o l l i s i o n energy of 2 KeVIAMU ( f i g . 4a and 4b). Considering

t h e 4 s 4 p and 4f-+d t r a n s i t i o n s i n t h e case o f a capture from He, t h e i r i n t e n -

s i t y r a t i o i s r e p r e s e n t a t i v e o f t h e r e l a t i v e p o p u l a t i o n o f 4s and 4 f and i s equal

t h e capture cross s e c t i o n t o 4s and 4f. The r a t i o o f

( qq c a l c u l a t e d t h e o r e t i -

o r d e r o f t h e t a r g e t i o n i z a t i o n p 8 t e n t i a l s r a t i /4/. T h i s comes from t h e f a c t t h a t a p a r t t h e 4p-)3s (case o f He) and 5 s and 4p-+3s (case o f Hz), a l l t h e o t h e r l e v e l s feed by cascade 3p; thus 3p+s represents w i t h i n t h e e r r o r ( n e g l e c t o f nu+s n >, 4) t h e t o t a l capture cross s e c t i o n ~~, 8+, ~, 7+.

These elements show t h a t from t h e spectroscopy w i t h t h e s c a l i n g s G e s e n t e d abo- ve, i t i s p o s s i b l e t o g e t a f u l l d e s c r i p t i o n o f t h e dynamics o f t h e c o l l i s i o n .

2 ) Less simple cases - I n so f a r , t h e above s p e c t r a show t h a t the l e v e l ( s ) most populated a r e p r e d i c t e d by t h e s c a l i n g (1).

I n t h e case o f far ^{example ~ 1 and ~ ~ ' 1} c o l l i d i n g on Hz, s h o ~ l d ^{~ '} be observed c a p t u r e t o n

5 (A1 ) and a s h a r i n g between n = 5 and n

4 (A1 ).

a) Case o f ~1~~ - Hz - I n t h i s case, l e v e l s and wavelengths o f t r a n s i t i o n s o f A1 V I I I above n

3 a r e n o t known /6/ /7/. To analyze t h e spectra, i t i s thus necessary t o perform a t h e o r e t i c a l c a l c u l a t i o n o f energy l e v e l s and associated wa- velengths w i t h n = 4,5 and 6. U t i l i z i n g an M.C.D.F. code, a check o f t h e accuracy o f t h e code i s performed r e c a l c u l a t i n g t h e known l e v e l s and t r a n s i t i o n s /8/. Then, c o n s i d e r i n g E-dipole t r a n s i t i o n s , t h e c a l c u l a t e d wavelengths a r e compared w i t h t h e observed t r a n s i t i o n s . I t i s then recognized t h a t a c e r t a i n number o f t h e s t r o n g e r t r a n s i t i o n s decay from n

5 and some l e s s i n t e n s e l i n e s a r e associated w i t h an i n i t i a l l e v e l n

6. The t r a n s i t i o n s from n = 4 a r e probably associated w i t h casca- des. T h i s i s shown i n f i g . 5 r e p r e s e n t i n g i n t h e form o f a G r o t r i a n diagram these rays.

6) Case o f *17' - H2 - I n t h i s case, A1 V I I , i n t h e e x i t channel i s N - 1 i - ke : regarding t h i s i o n data f o r e x c i t e d l e v e l s above n = 3 i s scarce. U t i l i z i n g c a l c u l a t e d l e v e l s and wavelengths /9/, t h e most i n t e n s e t r a n s i t i o n s a r e i d e n t i f i e d and a r e shown t o o r i g i n a t e from l e v e l s w i t h n = 5 and n = 4.

CONCLUSION

We have shown t h a t t h e o b s e r v a t i o n i n t h e X-UV range o f t h e low energy charge t r a n s f e r i n v o l v i n g h i g h l y charged i o n s c o n s t i t u t e an a l t e r n a t i v e method o f fundamen- t a l spectroscopy.

I t a l l o w s a n a l y s i s o f a f u l l r a d i a t i v e cascade o f an e x c i t e d i o n o f w e l l iden- t i f i e d mass and charge. Furthermore, s i n c e the most populated l e v e l ( s ) a r e p r e d i c - t e d a proper choice o f t h e t a r g e t g i v e s access t o h i g h l y e x c i t e d l e v e l s .

REFERENCES

/1/ R.K. JANEV and H.P. WINTER - Physics Reports 117 (5 & 6) 265 (1985)

/2/ S. BLIMAN, D. HITZ, B. JACQUOT, C. HAREL and A. SALIN - J . Phys .B : A t . Mol .

Phys. 16, 2849, 1983

/3/ R. MANN, H.F. BEYER, F. FOLKMANN - Physics o f E l e c t r o n i c and Atomic C o l l i s i o n s e d i t e d by S. DATZ, North-Holland, Amsterdam, 1982, p. 683

/4/ S. BLIMAN, M. BONNEFOY, J. J. BONNET, S. DOUSSON, A. FLEURY, D. HITZ and B. JAC- QUOT - Physica Scrypta T3, 63, 1983

/5/ H. JOUIN and C. HAREL - P r i v a t e communication

/6/ S. BASKIN and J.A. STONER J r - Atomic Energy l e v e l s and G r o t r i a n diagrams, American E l s e v i e r , New York, 1975

/7/ W.C. MARTIN and R. ZALUBAS - J. Phys. Chem. Ref. Data 8,850, 1979

f8/ M. MAYO, D. HITZ, M. DRUETTA, S. DOUSSON, J.P. DESCLAUX and S. BLIMAN - Phys.

Rev. L e t t . 54, 317, 1985

/9/ M. MAYO, D. HITZ, S. DOUSSON, J.P. DESCLAUX, S, BLIMAN and M. DRUETTA - J.

Phys. B : At. Mol. Phys. 18, L 539, 1985.

JOURNAL DE PHYSIQUE

F i g . l - T y p i c a l

- c o r r e c t e d s p e c t r a

6 10

i n t h e 6-11 nm wave- $

Fig. 2 - Population among s u b s t a t e s of c a p t u r e and lower l e v e l s f o r :

a ) ~ e + ~ He +

a) N.*+ ^{+ H p}

+ w

length range : 5

a ) Capture t o n

4 S ,.

b) Capture t o n

5 - ^qp

,I I I I I I I

f o r ~ e + ~ He. +

F i g . 5 - Griotrian type diagram f o r the most intense t r a n s i t i o n s observed in the decay following :

7+ +

~ 1 ~ ' + Hz -> ^A1 ( n l ) + ^{Hz where n = 5} i s the most popula-

ted 1 eve1 .

JOURNAL DE PHYSIQUE

Fig. 4 - Typical spectra obtained in the V.U.V. range showing cascade decay following :

a) nr8+ + ^H2 - - 3 . ~ r ~ + (nl) + H; (n = 5) b) ~ r + ~ He --\~r~+ + (nl ) + ^{He+ ( n}

⁴⁾

at E = 2 KeV / A.M.,U'..