N O T I C E
THIS DOCUMENT HAS BEEN REPRODUCED FROM
MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT
CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED
IN THE INTEREST OF MAKING AVAILABLE AS MUCH
INFORMATION AS POSSIBLE
(NASA-TPl-80666)
RATE
CCNSTANT
FOR
THE
MEACTIQN
OF
HYDROXYL
XADICAL
WITH
EBBHALDEHYDE
OV
Ell
THE
'IENFERBTUBE
RANGE
228-36
K
(NASA)
17
p
HC
A02/1F
A01
CSCk
Technical
Memorandum
Rate
Constant
for
the
Reaction
of
HydroxyB
Radical
with
Formaldehyde
Over
the
Temperature
Range
228-362K
.
L.
4.
Stief
Dm
Fa
Nava
W.
A.
i)ayne
J.
V.
Michael
MARCH
I980
Natntiona!
Aeronautics
and
Space
Administration
Q&d
$pmx
Flight
Center
Greenbelt,
Maryland
20771
RATE CONSTANT FOR
THE
REACTION OF HkDROXYL
RADICAI,
WITH
FORMALDEHkDE
OVER
THE TEMPERATURE RANGE 228-362
K
L.
J.
~tief,~
D.
F.
Nava,
h.
A.
Payne and
J.
V.
Michael
b
Astrochemistry Branch
Laboratory for Extraterrestrial Physics
NASA/Goddard Space Flight Center
Greenbelt, Maryland 20771
a)
Adjunct Professor of Chemistry, Catholic University of herica,
hashington,
D.
C.
20064
b)
Visiting Professor of Chemistry, Catholic University of America,
hashington,
D.
C.
20064
Absolute rate constants for the reaction
OH
+
H2C0 have been measured
over the temperature range 228-362K using the flash photolysis-resonance
fluorescence technique.
The results were independent of variations in
[H2CO],
total pressure
[Arj
and flash intensity (i.e., initial [OH]). The
rate
constant
was
found to be invariant with temperature in this range, the best
-11
3
-1 -1
representation being
k,
=
(1.05
+
0.11)
n
'iO
cm
~uolccule
s
where tho
error
is
two standard deviations. This result
is
compared with previous
absolute and relative determinations of
kl.
The reaction
is
also discussed
from a theoretical point of view.
The reaction of the hydroxyl radical with formaldehyde
is
of interest in
high temperature combustion studies, in an explanation for
CO
formation in
the atmosphere of Jupiter
,2
and in methane oxidation in the troposphere and
stratosphere of the
earth.3 in all these instances,
H2C0
is
a
product of
hydrocarbon
oxidatim.
For the Jovian atmosphere,
it
is
proposed that H2C0
is
formea primarily in the reaction
0
+
CH
Loss processes include photolysis
2
3
'
ana reaction with
H
and
OH.^^.
In the stratosphere,
H2C0
is
formed
as
a
proauct of the low temperature oxidation of atmospheric methane.
It
is
removed by photolysis and by reaction with
OH,
O
and
Ck.
The reactions
0
+
h2C0
and
Ck
+
H2C0
are relatively minor loss processes for formaldehyde
at
most altitudes in the stratosphere.' Rate constant measurements for these
reactions have been recently reported by us as
well
as other workers.
5,6
Reaction with
OH
is
a major sink for H2C0 at all altitudes in the upper
atmosphere,' but there have been no direct measurements of the absolute rate
constant
at
the low temperatures prevailing there.
The mechanism of the reaction has been usually assumed to be
H
atom
abstraction
OH
+
H2C0
+
H20
+
HCO,
(la)
although there
is
little
or no direct evidence for this. Recently, Horowitz
et
a1.7
have proposed the additional reaction channel
OH
+
H2C0
+
HCOOH
+
H.
(Ib)
Additional work
is
required to
test
the validity of this stlggestion.
Room temperature measurements of the absolute rate constant for the
react
ion
QH
a
H2C0
+
products (1
have been made using the discharge flow-mass spectrometric technique (DF-MS)
with
OH
in and by the flash ph~to~ysis-resonance fluorescence
technique
(FP-RF) with
H2C0
in excess.
Herron and
penzborn8 obtained a
3 -1 -1
-
9
lower
limit
kl
>
0.7 x cm molecule
s
,
Morris and Niki give kl
=
3 -1 -1
(
1.4
5
0.
x 0
c
molecule
s
and Atkinson and pittsl0 report kl
=
3 -1
-1
(0.94
5
0.10) x lo-''
cm
molecule
s
,
all
at
298
2
2
K.
There have been
three relative rate constant determinations at room temperature. Morris and
Niki,
l1
using the
DF-MS
technique, measured
OH
+
H2C0 relative to
OH
+
C
H
3 -1
-i
3
6
and obtained
the
result k1
=
(1.5
1.
0.15) x lo-''
cm
molecule
s
.
Niki et
a1.
l2
employed Fourier Transform Infra- red Spectroscopy
(FTIR)
with
OH
+
C
H
-11
3
2-1
as
the reference reaction and obtained k
-
(1.5
+
0.1)
IF
13 cm molecule
-
1
1
-
s
.
~mith'~ measured
OH
9
H2C0 relative to
OH
+
OH
using the DF-MS technique
-1 -1
and reports
kl
=
0.65 x 10-I
92
molecule
s
.
There have been only two variable temperature studies of the reaction,
10 10
one absolute
and one relative.
l3
Atkinson and Pitts
give k1
=
1.25
x
3
-1 -1
lo-" exp(-88
2
150/T)
cm
molecule
s
for the temperature interval
299
to
426
K
while ~mith'sl~ results from 268 to 334
K
may be represented by kl
=
6
x
3
10-I' exp(-635
2
250/T) cm molecule-' s-I.
This later study
is
the only one
below room temperature but
its.
usefulness
it:,
considerably reduced by the fact
that
the rate parameters of the rsference reaction
OH
+
OH
are
far
more
uncertain than those for
OH
+
H2Cc" itself.
An inspection of the available rate data thus shows disagreement
by
a
factor of two
at
room temperature,
a
factor
sf
five in the Arrhenius