BEAM FOIL- AND BEAM GAS- EXCITATION OF MONO- AND DI-ATOMIC PROJECTILES

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BEAM FOIL- AND BEAM GAS- EXCITATION OF MONO- AND DI-ATOMIC PROJECTILES

S. Schumann, H. Frischkorn, R. Kluge, D. Rosich, J. Schader, K. Groeneveld

To cite this version:

S. Schumann, H. Frischkorn, R. Kluge, D. Rosich, J. Schader, et al.. BEAM FOIL- AND BEAM GAS-

EXCITATION OF MONO- AND DI-ATOMIC PROJECTILES. Journal de Physique Colloques, 1979,

40 (C1), pp.C1-354-C1-355. �10.1051/jphyscol:1979177�. �jpa-00218457�

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JOURNAL DE PHYSIQUE Colloque C1, supplr5ment au n o 2, Tome 40, fPvrier 1979, page C1-354

S. Schumann, H. J. Frischkorn, R. Kluge, D. Rosich, J. Schader, K. 0. Groeneveld I n s t i t u t f a r Kernphysik der U n i v e r s i t z t Frankfurt/M, Germany

g6sum6. Des p r o j e c t i l e s moleculaires d ' e n e r g i e 1 MeV s o n t

tres

i o n i s e s e t t r e s excite% p a r i n t 6 r a c t i o n avec des c i b l e s gazeuses ou s o l i d e s . Aprss l a c b l l i s i o n , les fragments mol6culaires, charges positivement explosent p a t r~pulsion.Coulombienne et imposent l e u r cin4matique au rayonnement d e d e s e x c i t a t i o n par e f - f e t Doppler. Nous reportons i c i l a premi+re observation d'explosion Coulombienne a f f e c t a n t l a d e s e x c i t a t i o n p a r emission d ' 6 l e c t r o n Auger.

A b s t r a c t . Molecular p r o j e c t i l e s of ca. 1 MeV energy a r e highly e x c i t e d and highly ionized by t h e i n t e r - a c t i o n w i t h gaseous o r s o l i d t a r g e t s . A f t e r t h e c o l l i s i o n t h e positively-charged molecular fragments explode by t h e i r Coulomb r e p u l s i o n and impose t h e i r kinematics on t h e d e e x c i t a t i o n r a d i a t i o n v i a a Doppler e f f e c t . This paper r e p o r t s t h e f i r s t observation of Coulomb explosion e f f e c t i n g t h e d e e x c i t a t i o n by Auger e l e c t r o n emission.

INTRODUCTION from t h e t a r g e t ; t h i s y i e l d s information on meta-

The experimental observation of Coulomb s t a b l e s t a t e s w i t h a l i f e t i m e t i n t h e order of explosion of molecules a f t e r c o l l i s i o n s i n t h e t = V/X (Fig. 2 ) .

energy range around 1 MeV w i t h matter has been reported r e c e n t l y : 1. From molecular t a r g e t s a f t e r heavy-ion impact d e t e c t i n g t h e Auger e l e c t r o n emission [1,2], 2. from molecular beams measuring t h e kinematics of t h e exploding molecular fragments with high energy-and angular-resolution [ 3 ] and 3.

from molecular beams recording t h e electromagnetic d e e x c i t a t i o n r a d i a t i o n [41. This paper r e p o r t s 4.

from Coulomb explosion observed i n Auger e l e c t r o n s p e c t r a of beam f o i l - and beam gas- e x c i t e d molecular p r o j e c t i l e s .

EXPERIMENT

Auger e l e c t r o n energy s p e c t r a from mono-

+ +

atomic (N ) and diatomic (N2 ) n i t r o g e n p r o j e c t i l e s (57 keV/amu and 71 keV/amu) were measured a f t e r beam f o i l - and a f t e r beam gas- e x c i t a t i o n . A c y l i n d r i c a l n i r r o r analyzer in connection w i t h a c h a n n e l e l e c t r o n -.SmeCZS ei~CTXiKTnerg y-spPicProiileB€ e r [5]. The p r o j e c t i l e s i n t e r a c t e d w i t h a carbon f o i l (5 t o 10 ug/cm 2 ) o r gas t a r g e t s (He, N2, Ar a t t a r g e t pressure 10 mTorr). The chatge d i s t r i b u t i o n of t h e p r o j e c t i l e s was measured a f t e r t h e i r i n t e r a c t i o n with t h e gas t a r g e t a s a f u n c t i o n of t a r g e t p r e s s u r e i n o r d e r t o a s s u r e s i n g l e c o l l i s i o n s c o n d i t i p n s and s i n g l e charge s t a t e p r i o r t o t h e t a r g e t i n t e r a c t i o n .

Auger e l e c t r o n s p e c t r a were recorded from both N+ and N: a t t h e same p r o j e c t i l e v e l o c i t y v (Pig. 1). fn a d d i t i o n , s p e c t r a w e r e taken from Auger e l e c t r o n s emitted a t a d i s t a n c e x downstream

RESULTS

Figure 1 p r e s e n t s a t y p i c a l prompt ( i . e . x = 0) KU-Auger e l e c t r o n energy spectrum of mono- and diatomic n i t r o g e n i o n s e x c i t e d under s i n g l e c o l l i s i o n c o n d i t i o n s by N2-gas t a r g e t .

S i n c e too many d i f f e r e n t Auger t r a n s i t i o n s overlap i t i s d i f f i c u l t t o determine q u a n t i t a t i v e l y t h e l i n e width AE e s p e c i a l l y from t h e N2-data i n Fig. 1. Therefore, t h e delayed s p e c t r a ( i . e . x # 0) a s i n Fig. 2, have been used t o e x t r a c t t h e l i n e width AE s i n c e here, only few r a t h e r well-separated l i n e s a r e observed [5]. However, i n both c a s e s (Fig. 1 and Fig. 2) we observe c l e a r l y t h e much broader l i n e width from molecular p r o j e c t i l e s (N2) than from mono-atomic p r o j e c t i l e s

(k) .

The experimental l i n e width AE is composed of ( i ) n a t u r a l l i n e width, ( i i ) instrumental and geometrical l i n e broadening, ( i i i ) r e c o i l l i n e broadening and, i n t h e c a s e of molecular Auger e l e c t r o n emitters, (iv) Coulomb explosion broadening. A n a l y t i c a l d e t a i l s have been compiled e.g. i n [ 2 ] . It i s assumed t h a t t h e t o t a l width AEcalc can be c a l c u l a t e d by quadra- t i c a l l y summing over t h e i n d i v i d u a l c o n t r i b u t i o n s . Also, we o b t a i n t h e experimental c o n t r i b u t i o n of t h e Coulomb explosion a s displayed i n Table I by Q u a d r a t i c a l l y s u b t r a c t i n g AE (N2) and AE (N), without t h e d e t a i l e d bowledge of t h e c o n t r i b u t i o n ( i ) , ( i i ) and ( i i i )

.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979177

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I I I I I BEAM-GAS EXCITATION OF NITROGEN PRO3ECTILES

TARGET. N2 E I M = 7 l keVIAMU OBSERVATION ANGLE ~f

a I I I

320 360 400

C.M. ELECTRON ENERGY [ e ~ ]

-

F i g . 1. Auger e l e c t r o n s p e c t r a observed under 4Z0

+ +

from N2 and from N a t 7 1 keV/AMU e x c i t e d by N,-gas t a r g e t .

TARGET : N2 E I M r 7 l keVIAMU

,

⁶⁰⁰

w OBSERVATION ANGLE

z 2.

Z

. ..

^Ins^DELAYED

C.M. ELECTRON ENERGY [eV]

-

Fig. 2. Auger e l e c t r o n s p e c t r a observed under 42' from N ~ + and N

+

a t 71 keV/AMU ca. 1 nsec a f t e r e x c i t a t i o n by N 2- g a s t a r g e t .

TABLE I

Auger e l e c t r o n l i n e width c o n t r i b u t i o n by Coulomb e x p l o s i o n

T a r g e t Gas S o l i d

A E( eV) ~ ~ ~ 4.6

+

^0.5 ^3.9

⁺

^0.4

The c a l c u l a t e d c o n t r i b u t i o n t o t h e l i n e width by t h e Coulomb e x p l o s i o n i s given i n Ref. [ 2 ] . We f i n d a v e r y s a t i s f a c t o r y agreement between AEcalc and Al3 f o r beam gas e x c i t a t i o n (Table I).

exP

The AE v a l u e s i n s o l i d s and g a s e s should be t h e exp

same i n s t r a i g h t f o r w a r d c o n s i d e r a t i o n s . S u r p r i s - i n g l y , however, t h e LIE i n s o l i d s t e n d s t o be

exP

more t h a n 15% s m a l l e r than t h e v a l u e i n gases. We e x p l a i n t h i s by t h e wake p o t e n t i a l [3] which t e n d s t o a l i g n t h e l i n e a r molecule N2 i n t o t h e d i r e c t i o n of t h e beam, t h u s y i e l d i n g a kinematic broadening by t h e Coulomb e x p l o s i o n which o r i g i n a t e s o n l y f r o m t h e p r o j e c t i o n of t h e molecular fragment v e l o c i t y v e c t o r s i n t o t h e d i r e c t i o n of t h e e l e c t r o n d e t e c t o r . Assuming a complete alignment of t h e molecules we o b t a i n t h e v a l u e g i v e n i n b r a c k e t s i n Table 11.

CONCLUSIONS

Beam f o i l - and beam gas- Auger e l e c t r o n spectfoscopy of s w i f t molecular i o n beams y i e l d s r a t h e r d e t a i l e d - i n f o r m a t i o n of t h e Coulomb explo- s i o n i n g a s e s and i n s o l i d s . Also, t h e e l e c t r o n i c c o n f i g u r a t i o n s of t h e e x c i t e d s t a t e s involved

( h e r e mostly from Be-and B- l i k e systems) and t h e i r i n t e n s i t i e s can be s t u d i e d t o understand t h e e x c i t a t i o n mechanisms i n d i f f e r e n t c o l l i s i o n systems.

*

Supported by Bundesministerium flir Forschung und Technologie.

BIBLIOGRAPHY

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&,

68 (1977).

[2] R. Mann, F. Folkmann, R. S. P e t e r s o n , Gy. [ 5 1 S. Schumann, K. 0. Groeneveld, K. D. S e v i e r , Szab6, K. 0. Groeneveld, J. Phys. B (1978) B. Ericke, Phys. L e t t .

=,

289 (1977) and

t o b e published. r e f e r e n c e s quoted t h e r e i n .

[3] Z., Vager, D.-S. Gemmell, Phys. Rev. L e t t . 37, 1352 (1976) and r e f e r e n c e s quoted t h e r e i n .