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REACTIONS OF DOUBLY CHARGED IONS WITH VARIOUS NEUTRALS
K. Peska, E. Alge, H. Villinger, H. Störi, W. Lindinger
To cite this version:
K. Peska, E. Alge, H. Villinger, H. Störi, W. Lindinger. REACTIONS OF DOUBLY CHARGED IONS WITH VARIOUS NEUTRALS. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-21-C7- 22. �10.1051/jphyscol:1979710�. �jpa-00219069�
JOURNAL DE PHYSIQUE CoZZoque 67, suppZdment au n07, Tome 40, JuiZZet 1979, vape C7- 21
REACTIONS OF DOUBLY CHARGED IONS WITH VARIOUS NEUTRALS
K. Peska, E. Alge, H. Villinger, H. Stori and W. Lindinger.
I n s t i t u t ftir ExperimentaZphysik der LeopoZd Franzens UniversiMt ~ b t e i t u n g Atomhysik (HiiZZe J
,
Karl SchiinherrstraBe 3, A 6020 Innsbruck, Osterreich.
Recent i n v e s t i g a t i o n s o f r e a c t i o n s o f doubly charged i o n s / I - 5 1 have shown t h a t t h e y o c c u r i n most o f t h e c a s e s v i a s i n g l e c h a r g e t r a n s f e r and t h a t t h e y obey a c u r v e c r o s s i n g model, developed by Landau, Zener and S t u e c k e l b e r g ( s e e Ref. 1 )
.
S p e a r s e t a l . / I / , who have a p p l i e d t h i s model t o r e - a c t i o n s o f M ~ + + and ca++ c o u l d show, t h a t t h e r e a c t i o n s a r e f a s t , when t h e r e i s a c u r v e c r o s s i n g between t h e p o t e n t i a l c u r v e o f t h e r e a c t a n t s and t h e coulomb r e p u l s i o n c u r v e o f t h e p r o d u c t s ( F i g . 1 ) a t an i n t e r - n u c l e a r d i s t a n c e of a fewa.
POTENTIAL ENERGIES
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F i g . 1
I n o r d e r t o g e t more i n s i g h t i n t o t h e mechanism of t h e r e a c t i o n s of doubly
charged i o n s , we have i n v e s t i g a t e d many o f them a s a f u n c t i o n of t h e r e l a t i v e k i n e t i c e n e r g y KEcm o f t h e r e a c t a n t s ( t h e r m a l t o a few eV) i n a d r i f t e x p e r i m e n t / 2 , 5 / . Most of t h e r e a c t i o n s w i t h m o l e c u l a r r e a c - t a n t s t u r n e d o u t t o be f a s t and indepen- d e n t of K E m . T h i s i s u n d e r s t a n d a b l e due t o t h e f a c t t h a t most m o l e c u l a r i o n s h a v e a wide v a r i e t y o f h i g h l y i n g e l e c t r o n i c s t a t e s w i t h many v i b r a t i o n a l l e v e l s , s o
t h a t i n many c o m b i n a t i o n s o f doubly c h a r g e d i o n s and m o l e c u l a r r e a c t a n t s , c u r v e c r o s s i n g s o c c u r i n t h e p r o p e r i n - t e r n u c l e a r d i s t a n c e , t h u s l e a d i n g t o a h i g h r e a c t i o n p r o b a b i l i t y . A s an example f o r s u c h a c a s e , w e show i n F i g . 2 t h e en-
+
3e r g y dependence o f t h e r e a c t i o n Ne ( P ) + N 2 '
F i g . 2
The s i t u a t i o n i s q u i t e d i f f e r e n t , when H 2 o r a r a r e g a s i s chosen a s t h e n e u t r a l r e a c t a n t . The ~ ~ + - ~ y s t e m h a s a wide r a n g e from 18.2 eV t o a b o u t 28 eV i n t h e Franck-
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979710
Condon-regime, w h e r e n o e l e c t r o n i c s t a t e s e x i s t , a n d t h e rare g a s i o n s ( s i n g l y c h a r g e d ) h a v e e x c i t e d s t a t e s o n l y h i g h a b o v e t h e i o n i c g r o u n d s t a t e , s o t h a t t h e c o n d i t i o n s f o r a c u r v e c r o s s i n g a t a n i n t e r n u c l e a r d i s t a n c e o f a few
2
i s m e t o n l y i n a few c a s e s . I n t h e r e a c t i o n+ +
~ r + + ( I S )
+
H e + A r+
H e t h e c u r v e c r o s s i n g o c c u r s a t 2 . 0 2 which i s t o o c l o s e t o a l l o w f o r a h i g h r e a c t i o n p r o b a - b i l i t y a n d t h u s t h e r e a c t i o n r a t e c o n s t a n t i s v e r y s m a l l (k < 10-I c m 3 s e c - I ).
A ~ + + ( ~ P ) r e a c t s w i t h H e w i t h a t h e r m a l r a t e c o n s t a n t o f a b o u t 5 . 5 x 10-I lcm 3 sec-'
,
t h e r e s p e c t i v e c u r v e c r o s s i n g b e i n g a t 4.58.
A s F i g . 2 shows, t h e r e i s a d i s t i n c t i v e i n c r e a s e o f t h e r a t e con- s t a n t f o r t h i s r e a c t i o n w i t h i n c r e a s i n g r e l a t i v e k i n e t i c e n e r g y KEcm o f t h e r e a c t a n t s . An i n c r e a s e o f KEcm means a s h i f t o f t h e c u r v e c r o s s i n g p o i n t t o s a m l l e r i n t e r n u c l e a r d i s t a n c e s . From t h e s e r e s u l t s o n e h a s t o assume t h e maxi- mum o f t h e r e a c t i o n p r o b a b i l i t y f o r t h e above t y p e o f r e a c t i o n t o o c c u r b e t w e e n 2 a n d 4.5 2. T h i s a g r e e s w e l l w i t h re- s u l t o f J o h n s e n a n d B i o n d i , who f o u n d A ~ + + ( ' D ) t o r e a c t q u i t e f a s t ( k = 1 0 - l o cm3 s e c - I ) w i t h H e . The c u r v e c r o s s i n g i s a t 2 . 88
i n t h i s c a s e .S e v e r a l more r e a c t i o n s w i l l b e d i s c u s s e d i n view o f t h e c u r v e c r o s s i n g model a n d
++
3r e s u l t s o f t h e r e a c t i o n s o f A r ( P),
~ r + + ( I S ) and ~ e + + ( 3 ~ ) w i t h v a r i o u s neu- t r a l s w i l l b e shown.
The " G s t e r r e i c h i s c h e r Fonds z u r F d r d e r - un9 d e r w i s s e n s c h a f t l i c h e n Forschung" i s t h a n k e d f o r s u p p o r t t h r o u g h p r o j e c t NO S 1 8 / 0 7 .
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2919 ( 1 9 7 7 )/ 6 / W. L i n d i n g e r , E. A l g e , H . S t d r i , R . N . Varney, H . H e l m , P . Holzmann a n d M. P a h l , 1 n t . J . Mass Spectrom.
I o n Phys. i n p r e s s ( 1 9 7 9 ) .