THE INFLUENCE OF ION VIBRATIONAL EXCITATION ON ION MOLECULE REACTIONS

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THE INFLUENCE OF ION VIBRATIONAL EXCITATION ON ION MOLECULE REACTIONS

E. Alge, H. Villinger, K. Pesca, H. Ramler, H. Störi, W. Lindinger

To cite this version:

E. Alge, H. Villinger, K. Pesca, H. Ramler, H. Störi, et al.. THE INFLUENCE OF ION VIBRA-

TIONAL EXCITATION ON ION MOLECULE REACTIONS. Journal de Physique Colloques, 1979,

40 (C7), pp.C7-83-C7-84. �10.1051/jphyscol:1979741�. �jpa-00219410�

JOURNAL DE PHYSIQUE Cc)Zloque C7, suppldment

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n07, Tome 40, JuiZZet 1979, Page C7- 83

THE IWLUENCE OF ION VIBRATIONAL EXCITATION ON ION MOLECULE REACTIONS

E. Alge, H. Villinger, K. Pesca, H. Rarnler, H. Stori and W. Lindinger.

T n s t i h t fur ExperhentaZphysik der LeopoZd Franzens Universitat, Abteilung Atomphysik (WZ Ze)

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Karl Sehijnherrstrasse 3

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A 6020 InnsGruck, Osterreich.

The mean k h e t i c e n e r g y KEion o f i o n s d r i f t i n g 2n a b u f f e r g a s u n d e r t h e i n - f l u e n c e o f a n e l e c t r i c f i e l d i s w e l l r e - p r e s e n t e d by t h e Wannier e q u a t i o n

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where vd i s t h e d r i f t v e l o c i t y o f t h e i o n s a n d mi and mm a r e t h e i o n a n d b u f f e r masses r e s p e c t i v e l y .

On t h e o t h e r hand s o f a r t h e r e o n l y ex- ists a q u a l i t a t i v e p i c t u r e upon t h e i n t e r n a l v i b r a t i o n a l e n e r g y o f m o l e c u l a r i o n s S r i f t i n g i n a b u f f e r g a s . R e c e n t NOAA-results / 2 / a n d r e s u l t s o b t a i n e d i n o u r l a b o r a t o r y h a v e shown, t h a t molecu- l a r i o n s s u c h a s 02+ a n d

co2+

a r e v i b r a - t i o n a l l y e x c i t e d more r e a d i l y when d r i f - t i n g i n a n a r g o n b u f f e r t h a n i n a h e l i u m buffer. T h i s was d e m o n s t r a t e d by i n - v e s t i g a t i n g i n a n a r g o n a n d h e l i u m b u f f e r t h e e n e r g y d e p e n d e n c e s of t h e r a t e con- s t a n t s of i o n m o l e c u l e r e a c t i o n s which

s t r o n g l y depend o n t h e v i b r a t i o n a l e n e r g y o f t h e i o n s . The r e a c t i o n o f O 2

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w i t h C H 4 i s s l o w a t room t e m p e x a t u r e ( k = 6x10-l2 cm3 s e c - I ) a n d h a s a main e x o t h e r m i c r e a c t i o n c h a n n e l i n t o 0 2 c H 3 + , b u t a t e l e - v a t e d e n e r g i e s (KEcm, t h e r e l a t i v e k i n e t i c e n e r g y o f t h e r e a c t a n t s i s o b t a i n e d by c o n v e r s i o n o f t h e i o n k i n e t i c e n e r g y i n t o t h e c e n t e r o f mass e n e r g y i n t h e u s u a l way / 3 / ) t h e s l i g h t l y e n d o t h e r m i c r e a c - t i o n c h a n n e l s t o C H ~ + a n d c H 4 + among other: become a v a i l a b l e . A c c o r d i n g t o t h e o e t i c a l c o n s i d e r a t i o n s o f P o l a n y i a n d c o w o r k e r s / 4 , 5 / t h i s t y p e of r e a c t i o n s h o u l d b e promoted by v i b r a t i o n a l e x c i t a - t i o n . I n f a c t t h e r a t e c o n s t a n t f o r t h e r e a c t i o n o f 02+ w i t h CH4 shows a much s t r o n g e r i n c r e a s e a t e l e v a t e d e n e r g i e s i n a n a r g o n t h a n i n a h e l i u m b u f f e r / 6 / .

F i g . 1 F i g . 2

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979741

I n t h e p r e s e n t i n v e s t i g a t i o n w e compare the r e s u l t s on t h e e n e r g y dependences of t h e r e a c t i o n of O 2

+

w i t h CH4 o b t a i n e d i n a helium, an argon and a C02 b u f f e r , and o f t h e r e a c t i o n s o f C02 w i t h O2

+

and D2 o b t a i n e d i n h e l i u m , neon and a r - gon. I n t h e c a s e of O 2

+ +

CH4 o u r r e - s u l t s o b t a i n e d i n helium and a r g o n a g r e e w e l l w i t h t h e NOAA r e s u l t s / 6 / , a s can b e s e e n i n F i g . 1 . The r e s u l t s o b t a i n e d i n C02 show t h a t t h i s b u f f e r i s l e s s e f f e c t i v e i n v i b r a t i o n a l l y e x c i t i n g O 2 t h a n argon b u t i s o b v i o u s l y more e f f e c - t i v e t h a n helium. The r e s u l t s f o r t h e r e a c t i o n o f C02 w i t h 0 2 , which

+

i s a l s o promoted by v i b r a t i o n a l e x c i t a t i o n of t h e r e a c t a n t i o n a r e shown i n F i g . 2 t o g e t h e r w i t h d a t a o b t a i n e d i n a h e l i u m and an a r g o n b u f f e r a t NOAA / 7 / .

co2+ +

D p

i s a r e a c t i o n , which i s slowed down

F i g . 3

by v i b r a t i o n a l e x c i t a t i o n and o u r r e - s u l t s a r e shown i n F i g . 3 . From t h e r e - s u l t s o f F i g s . 2 and 3 one can assume, t h a t r a r e g a s e s have a h i g h e r e f f i c i e n c y f o r e x c i t i n g v i b r a t i o n a l e x c i t a t i o n of m o l e c u l a r i o n s t h e h e a v i e r t h e a t o m i c mass o f the rare gas atoms is. T h i s i s

a t l e a s t t h e c a s e f o r He, Ne, and A r . On t h e o t h e r hand, when o t h e r ga$es i n - s t e a d o f r a r e g a s e s a r e u s e d a s a b u f f e r , no such s t a t e m e n t can b e made

as

i s s e e n from t h e examples of F i g . 1 .

The " O s t e r r e i c h i s c h e r Fonds z u r Forder- und 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 under c o n t r a c t No. S 18/07.

/ I / G . H . Wannier, B e l l S y s t . Tech. J . 32, 170 (1953)

-

/ 2 / D.L. A l b r i t t o ~ NATO advanced s t u d y i n s t i t u t e , La Baule 1978

/3/ M . M c F a r l a n d , D.L. A l b r i t t o n , F.C.

F e h s e n f e l d , E.E. Ferguson and A.L.

Schmeltekopf, J.Chem.Phys.

59,

⁶⁶²⁰

(1973)

/ 4 / J . C . P o l a n y i and W.H. Wong, J.Chem.

Phys.

5 ,

1439 (1969)

/5/ M.H. Mok and J . C . P o l a n y i , J.Chem.

Phys.

51,

1451 (1969)

/6/ I . Dotan, F.C. F e h s e n f e l d and D.L.

A l b r i t t o n . J.Chem.Phys.

68,

⁵⁶⁶⁵

(1978)

/ 7 / W. L i n d i n g e r , M.Mc F a r l a n d , F.C.

F e h s e n f e l d , D.L. A l b r i t t o n , A.L.

Schmeltekopf and E . E . Ferguson, J . Chem-Phys.

63,

2175 ( 1 9 7 5 ) .

These i n v e s t i g a t i o n s w i l l b e c a r r i e d on and w i l l b e e x t e n d e d t o a k r y p t o n b u f f e r .