13 Infrared Chemiluminescence from F + R H and H + ClF Reactions KEIETSU TAMAGAKE and D. W. SETSER
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Department of Chemistry, Kansas State University, Manhattan, KS 66506
Infrared emission s p e c t r a from newly formed HF and HCl product molecules were observed under n e a r l y a r r e s t e d r e l a x a t i o n c o n d i t i o n s w i t h a c o l d w a l l r e a c t i o n vessel at 77°K and a D i g i l a b F o u r i e r Transform Spectrometer. The r e a c t i o n s examined were F + HCl, HBr, HI, H S, GeH , CH , CH CH , CH3Cl, CH Br, C(CH ) , CH OCH (plus some others not reported here) and H + ClF. The flow r a t e s and pressure i n the vessel were 0 . 5 - 3 0 µmol/sec and 0 . 5 - 5 x 10 torr, r e s p e c t i v e l y . These experiments are an improvement over previous work from t h i s l a b o r a t o r y and permit assignment o f both the initial v i b r a t i o n a l and r o t a t i o n a l distributions o f the HF and HCl product m o l e c u l e s . 2
3
4
4
3
3
3
3 4
3
-5
F + RH The data from the F + HCl r e a c t i o n gave virtually the same v i b r a t i o n a l and r o t a t i o n a l d i s t r i b u t i o n s as p r e v i o u s l y reported (1). However, our r e s u l t s f o r the F + HBr and F + HI r e a c t i o n s have g r e a t e r populations i n the highest v i b r a t i o n a l l e v e l s than the previous r e p o r t ( 2 ) , which was based on e x t r a p o l a t e d distributions i n a 1 torr fast flow r e a c t o r . With a few e x c e p t i o n s , the highest observed vibrational-rotational level i s that permitted by the thermochemistry. In some cases the thermochemical limit i s so c l o s e to v t h a t only a few r o t a t i o n a l l e v e l s are permitted and the relative p o p u l a t i o n of v i s low; an example is HCl f o r which o n l y J = 8 is permitted i n the v=3 level. A similar l i m i t holds f o r F + GeH . There a l s o can be dynamical limitations such as f o r F + toluene ( 3 ) . The most h i g h l y populated r o t a t i o n a l l e v e l s are at high J f o r the diatomic c a s e s , but f o r the polyatomic cases low J l e v e l s are favored. Initial vibrational distributions, P, and the f r a c t i o n s o f the t o t a l a v a i l a b l e energy released to vibration, , and rotation, , of HF are listed i n Table I . The reduced r o t a t i o n a l energy f o r i n d i v i d u a l vibrational states =/, and reduced t o t a l r o t a t i o n a l energy = / a l s o are l i s t e d . From the t a b l e s the f o l l o w i n g c o n c l u s i o n s can be reached. (A) The v i b r a t i o n a l d i s t r i b u t i o n s P and are s i m i l a r f o r both diatomic and max
max
4
v
V
(v)
R
R
(v)
R
V
v
124
Brooks and Hayes; State-to-State Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
Brooks and Hayes; State-to-State Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
V
Ρ
ν= ν= ν = ν =
V = V =
ν = ν = ν = ν=
1 2 3 4 5 6
1 2 3 4 5 ν = ν = 6
kcal mole -1
.25 .30 .26 .24
.28
.29 .33 .37 .40 .45 .47 .40
.30 .35 .38 .42
.35
.43 .40 .52
.35
.15
.24 .11 .10
.62 .058
.14
.24 .13 .08
.61 .055
.23
.32 .26 .13
.69 .070
.65 .14
.63 .13
.57 .12
.09 .36 .55
.12 .46 ,42
.18 .69 • 14
.23 .25 .34 .18
.10 .12 .13 .16 .22 .28
.12 .17 .30 .41
.25 .63 .11
.57 .15
39
3
CH C1
41
CH3CH3
35
CH. 4
47
2
HS
67
HI
51
HBr
36.5
HC1
.21
.25 .22 .13
.049
.039 .058 .015
.43 .50 .42 .26 .26
.42
.17 .17 .17
.17
.57 .18 .54 .022
.51 .084
.67 .069
.14 .20 .28 .37 .02 .27 .38 .35
.19 .64 .16
GeH. 4
.11 .45 .44
2
55
3
(CH ) 0
45
4
40
3
C(CH )
38
3
CH Br
Table I. Summary of Vibrational and Rotational Energy Disposal
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STATE-TO-STATE CHEMISTRY
polyatomic reagents. (B) The < f > i s high ( 0 . 1 3 - 0 . 1 7 ) f o r diatomic and low (0.05-0.08) f o r polyatomic cases. (C) The t r i a t o m i c mole c u l e HpS gives intermediate (0.12). (D) the Gehty r e a c t i o n i s unusual and gives e x c e p t i o n a l l y high l i k e a diatomic case. (E) The values i n c r e a s e w i t h ν f o r diatomic r e a c t a n t s and decreases f o r polyatomic r e a c t a n t s . (F) The o v e r a l l f o r d i a tomic, t r i a t o m i c and some polyatomic reagents ( C H 3 C I , Cr^Br) are c l o s e to 0 . 4 , 0 . 2 9 , and 0 . 2 5 , r e s p e c t i v e l y . Such values are expected i f the remaining energy, a f t e r s u b t r a c t i o n o f the f r a c t ion r e l e a s e d t o v i b r a t i o n of HF, i s d i s t r i b u t e d s t a t i s t i c a l l y be tween the 2 r o t a t i o n s o f HF, the 3 r e l a t i v e t r a n s l a t i o n s plus 2 or 3 r o t a t i o n s of the parent r a d i c a l ( f o r t r i - or polyatomic reagent, respectively). (G) The hydrocarbons C H 4 , C H and 0 ( ^ 3 ) 4 give s m a l l e r than the expected value based upon the above model f o r a polyatomic reagent. (H) The f o r GeH^ i s as high as a diatomic reagent. R o t a t i o n a l r e l a x a t i o n may be more s i g n i f i c a n t f o r CH* and C£Hg because of the r e l a t i v e l y high vapor pressure a t 77°K. The low f o r C(CHo)^, as well as the non l i n e a r s u r p r i s a l p l o t ( 3 J , may be a t t r i b u t e d to c o l l i s i o n dynamics which t r a n s f e r s e n ergy to v i b r a t i o n s o f the parent r a d i c a l . I n t e r p r e t a t i o n o f the (CHoJpO r e s u l t s must be done w i t h caution because o f the r a d i c a l s t a b i l i z a t i o n energy, which reduces the o v e r a l l a v a i l a b l e energy (4). The d i a t o m i c - l i k e behavior of GeH^ may be explained by the very l a r g e r e a c t i v e cross s e c t i o n , which i s more than 7 times l a r g e r than F + CH^ ( 5 j . Such a l a r g e cross s e c t i o n allows the hydrogen atom to move from GeH^ to the F atom w i t h an impact parameter t h a t i s l a r g e enough to keep the parent r a d i c a l GeH3 unexcited by the i n t e r a c t i o n w i t h the newly formed HF molecule. R
R
R
v
R
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2
6
R
R
R
H + Cl F This r e a c t i o n gave emission from HF and HC1. Using the l a t e s t E i n s t e i n c o e f f i c i e n t , the r a t i o o f kHF d kHCl ob t a i n e d as 1 to 3 . 9 . The values f o r HF and HC1 are 0.53 and 0 . 4 4 , r e s p e c t i v e l y . The HF r o t a t i o n a l d i s t r i b u t i o n i s very broad and much more extended than from H + F . a n
w
a
s
v
2
Literature Cited 1) 2) 3) 4) 5)
Ding, A.M.G., Kirsch, L.J., Perry, D . S . , Polanyi, J . C . and Schreiber, L., Faraday Disc. Chem. Soc. (1973) 55, 252. Jonathan, N . , Melliar-Smith, C . M . , Okuda, S., Slater, D . H . , and Timilin, D . , Mol. Phys. (1971) 22, 561. Bogan, D . J . and Setser, D.W., J. Chem. Phys. (1976) 64, 586. Bogan, D . J . , Setser, D.W., and Sung, J.P., J. Phys. Chem., May (1977). Smith, D . J . , Setser, D.W., Kim, K.C. and Bogan, D.J., J. Phys. Chem., May (1977).
Brooks and Hayes; State-to-State Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
