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4,,
ABSOLUTE RATE OF THE REACTION
OF C
1
(
2
P) WITH METHANE
FROM 200-500K
(NASA-TM-X-71221)
ABSOLUTE RATE OF THE
N77-11136
REACTIGN OF C L(2P) WITH METHANE FROM
200-500 K (NASA)
25 g HC A02/MF A01
CSCL 07D
"Inclas
G3/23 55739
D. A. WHYTOCK
J. H. LEE
3
J. V. MICHAEL
W. A. PAYNE
L. J. STIEF
^.
DEC 1976,
RECEIVED+'
NASA
OCTOBER 1976
`'
s^
EWIUIT
INPUT BRANCH \
1
^^yh
GODDARD SPACE FLIGHT CENTER
GREENBELT, MARYLAND
I
i
ABSOLUTE 2ATE OF THE REACTION OF' :;L(2P)
WITH METHANE FROM 2,j0-500K
.
I
Do A. Whytock
Department of Chemistry
University of Essex
Colchester, Essex
and
Jo Ho Lee**, J. V. Michael***,
W. A.
Payne and Lo Jo Stief
Astrochemistry Branch
Laboratory for Extraterrestrial Physics
NASA/Goddard Space Flight Center
Grec nbelt, Y-ryla nd 20771
*On leave 1975--76 at Catholic University of America,
Washington, D.C. 27017
**NAS/NRC Resident Research Associate
***NAS/NRC Senior Resident Research Associate
+Al G
k
i
-
.F
12
Rate Constants for the reaction of atomic chlorine
with methane have been measured from 200-500K using the
I
flash photolysis-resonance fluorescence technique. When
the results from fourteen equally spaced experimental
ttt]]]
determinations are plotted 'n Arrhenius form a definite
curvature is noted. The results are best represented by
16.34
1
--
the least squares equation, k = (5.44 + 4.08) x 10
-i9
T
(2.50 + 0.21) exp (-608+62/T) cm molecule
-1
s
-1
,
The
results are compared to previous work and are theoretically
discussed.
P!
INTRODUCTION
Rate constants for the reaction of chlorine atoms with
hydrogenous species are of great current interest due to the
potential importance of such reactions in determining the
rate of ozone depletion in the earth's ^rratosphere
l
. Thus,
termination of C
,
^, atom chains in the stratosphere can occur
via
C't + RH --) HC-f, + R
(1)
which woald result, at least temporarily, in the destruction
of CL atoms and interruption of the Ct,-CZO chain which
destroys ozone. The reaction of CZ atoms with CH
4
is of
particular importance in this respect because of its
abundance in the stracospherel,
Until very recently, only three direct studies had
been made of the rate constant for the reaction
Ct
Davis, Braun and Ba„s2
x 10
-13
cm molecule-1
resonance fluorescence
+ CH
4
- HCl + CH
3
(2)
reported a value of k
2
= (1,5+0.'-)
S
-1
at 298K using the flash photolysis-
(FP-RF) technique. Clyne and Walker
A
4
measured k
2
using a discharge flow - :Hass spectrometric
(DF-MS) technique and obtained k
2
= (5,08+0.53) x 10-11
exp(-1790+40/T)
em
molecule-1 s
-1
from 300-686K, while
1
s,