HAL Id: jpa-00219163
https://hal.archives-ouvertes.fr/jpa-00219163
Submitted on 1 Jan 1979
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
NON-EQUILIBRIUM DISSOCIATION PHENOMENA
W. Bailey, A. Garscadden
To cite this version:
W. Bailey, A. Garscadden. NON-EQUILIBRIUM DISSOCIATION PHENOMENA. Journal de
Physique Colloques, 1979, 40 (C7), pp.C7-377-C7-378. �10.1051/jphyscol:19797185�. �jpa-00219163�
JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 2979, page C7- 377
NON-EQUILIBRIUM DISSOCIATION PHENOMENA
W.F. Bailey and A. Garscadden.
Air Force Aero Propulsion Laboratory, Wright-Patterson Air Force Base, Ohio, U.S.A. 45433.
A comprehensive a n a l y s i s of c o l l i s i o n a l l y high temperatures where m u l t i p l e quantum V-T t r a n s - induced d i s s o c i a t i o n (Eqn. 1) under e q u i l i b r i u m i t i o n s begin t o c o n t r i b u t e . The r e s u l t s show t h a t and nonequilibrium c o n d i t i o n s has been performed1! t h e s t a n d a r d laddermodel p r e d i c t s d i s s o c i a t i o n S o l u t i o n s of t h e s e t of coupled n o n - l i n e a r d i f f e r - r a t e s t h a t a r e t o o low and t h a t r o t a t i o n a l e f f e c t s e n t i a l e q u a t i o n s (Eqn. 2) f o r each of t h e v i b r a - must b e included i n t h e model. Agreement i s t i o n a l l e v e l s and t h e continuum,known a s t h e f u r t h e r improved by i n c l u d i n g equal energy t r a n s - Master equation,have been achieved f o r both s t e a d y i t i o n s i n v o l v i n g a quasi-bound v i b r a t i o n a l - s t a t e and time-dependent c o n d i t i o n s . r o t a t i o n a l l e v e l (Fig. 2)
AB(v,J) + M 3 A+B+M (1) As an example, d i s s o c i a t i o n r a t e s were
N1 denotes t h e c o n c e n t r a t i o n o f molecules i n s t a t e 1, and t h e R ' s r e p r e s e n t g e n e r a l i z e d r a t e c o e f f i c - i e n t s f o r t h e p o p u l a t i o n o r depopulation of s t a t e 1 involved i n c o l l i s i o n a l energy exchanges between s t a t e s i, j and k. The Master equation was solved under t h e p h y s i c a l l y r e a l i s t i c assumptions t h a t 1 ) t h e t r a n s l a t i o n a l and r o t a t i o n a l degrees o f freedom a r e i n complete Boltzmannequilibrium.
2 ) t h e molecules i n each v i b r a t i o n a l s t a t e a r e t r e a t e d a s s e p a r a t e s p e c i e s . 3) only s i n g l e quantum v i b r a t i o n a l exchanges occur. 4) t h e molecule i s r e p r e s e n t e d a s a Morse o s c i l l a t o r
1017
-
o21016 -
CHEMICAL €0.
I I I
REGIME j GNC
TIME[SEC]
Flg 1 1)me ~roflles and Unl.mretl~md Flu*
r i g i d r o t a t o r system. The time dependent s o l u t i o n
I
f o r thermal d i s s o c i a t i o n c o n d i t i o n s ( e . g . , shock h e a t i n g , 4 0 0 0 ~ ~ ) h a s e s t a b l i s h e d t h a t t h e v i b r a -
' I
t i o n a l energy d i s t r i b u t i o n , VED, r a p i d l y a t t a i n s
a pseudo-steady s t a t e (Fig. 1 ) . This s t e a d y s t a t e
b'
d i s t r i b u t i o n d e v i a t e s from t h e e q u i l i b r i u m d i s t r i -
Fig 2a Fig. 2b Flg. 20
Flg. 2 Alternate Paths for Dorsosiatton
b u t i o n because o f v i b r a t i o n a l - d i s s o c i a t i o n coupl-
d e r i v e d f o r t h e h i g h l y non-equilibrium c o n d i t i o n s i n g . That is, t h e d e p l e t i o n of high l e v e l
t h a t occur i n carbon monoxide d i s c h a r g e s . Heavy p o p u l a t i o n s s u b s t a n t i a l l y reduces t h e d i s s o c i a t i o n
p a r t i c l e and e l e c t r o n impact d i s s o c i a t i o n have r a t e from t h a t which would b e o b t a i n e d i f t h e
been compared (Fig. 3 ) . The d i s s o c i a t i o n due t o coupling were n o t considered. A comparison of
e l e c t r o n impact was d e r i v e d u s i n g a s t e a d y s t a t e i n d u c t i o n times gave good agreement except a t v e r y
s o l u t i o n of t h e c o l l i s i o n a l Boltzmann e q u a t i o n .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797185
3 s 7 18 2a 38 118 V N CTPHNSEND)
Fig. 3 Comparison of Electron and Heavy Particle D#ssociat~on
This showed t h a t t h e e f f e c t i v e d i s s o c i a t i o n con- s t a n t is a s t r o n g l y i n c r e a s i n g f u n c t i o n o f E/N and it i s a l s o enhanced by s u p e r e l a s t i c c o l l i s i o n s and by t h e reduced d i s s o c i a t i o n t h r e s h o l d of t h e v i b r a - t i o n a l l y e x c i t e d s p e c i e s . Examination of t h e heavy p a r t i c l e k i n e t i c s r e v e a l e d t h e temporal development of t h e t h r e e c h a r a c ~ e r i s r i c r e g i o n s of t h e V E ~ . The c a l c u l a t e d VED showed good agreement w i t h t h e experimental d a t a of ~ i c h ( ~ ) . The p r e d i c t i o n s a r e t h a t e l e c t r o n impact d i s s o c i a t i o n always dominates t h e heavy p a r t i c l e r a t e f o r d i s c h a r g e s o f i n t e r e s t i n carbon monoxide. However, experiments have a l s o been made r e c e n t l y on o p t i c a l l y pumped d i s s o c i a t i o n of carbon monoxidec2). C a l c u l a t i o n s made with t h e models f o r t h e s e c o n d i t i o n s y i e l d e d d i s s o c i a t i o n r a t e s t h a t appear t o be much lower than t h o s e i n d i c a t e d by t h e s e experiments (Fig. 4 ) . We
t h e r e f o r e propose t h a t a more e f f i c i e n t channel f o r CO d i s s o c i a t i o n must e x i s t . A l t e r n a t i v e p r o c e s s e s t h a t appear t o s a t i s f y t h e experimental observa- t i o n s a r e (a) multi-quantum V-V exchange and/or
(b) v i b r a t i o n a l t o e l e c t r o n i c , V-e exchange : CO(V) + C O ( V ' ) +
c
+ 0*
CO(V") (3) co(v) + c o ( v t ) + co* + c o ( v l " ) (4a)co* + co(v) 4
co2
+c
(4b)The observed i s o t o p i c enhancement i n d i s s o c i a t i o n p r o d u c t s , t h e s i m i l a r dependence on t h e Treanor o r
Fig. 4 Optical Pumping, Heavy Partical Dissociation Constant
p l a t e a u r e g i o n s of t h e VED and t h e r e f o r e a l s o t h e , pumping and t h e temperature dependencies, w i l l n o t g i v e t h e r e l a t i v e importance of t h e mechanisms.
However, t h e primary d i s s o c i a t i o n p r o d u c t s (Eqns.
(3) and (4b)) should be i d e n t i f i a b l e by mass- spectroscopy. The p r e s e n c e of 0 2 would f a v o r t h e V-V mechanism whereas t h e presence o f C02 would t e n d t o i n d i c a t e t h e dominance of t h e V-e e x c h a n ~ e .
I n a d d i t i o n , t h e a c t i v a t i o n e n e r g i e s f o r t h e V-V and V-e mechanisms d i f f e r : f o r t h e V-V, EV+E d D o where D = l l e V , w h i l e f o r V-e,EV+E$-E* where E* i s
0
t h e energy of t h e r e a c t i n g e l e c t r o n i c s t a t e , 6.2eV f o r CO(a 3 TI). Thus i t should be p o s s i b l e t o d i s -
t i n g u i s h between t h e two mechanisms by t i t r a t i n g helium t o a l t e r t h e VED and simultaneously monitor-
i n g t h e Swan band i n t e n s i t y (from C + C +C2*
-+
C 2 + h*) t o e s t a b l i s h t h e dependence of k w i t h t h e D
l o c a t i o n of t h e "knee1' o f t h e VED.
1 . W. F. Bailey, PhD T h e s i s , US A i r Force I n s t i - t u t e of Technology, (1978).
2. Rich, J . W., R. C. Bergman, and M. J . Williams
"Measurement o f K i n e t i c Rates f o r Carbon Monoxide Laser System." Calspan Report No. 1VG-6021-A-1, November (1977).
