192
E.W. Kaiser, T.J. Wallington / Chemical Physics Letters 501 (2011) 187–192
from Figure 5, the values of k1/k3 measured at the upper end of the
2.0
1.5
GC
FTIR
temperature range studied by Caecero-Vega et al. [1] are actually
lower than the values we measured and a simple heterogeneous
loss of propene can not be invoked as the explanation of the dis-
crepancy between the studies.
Coquet and Ariya
Caecero-Vega et al.
We report a large body of self-consistent data concerning the
kinetics of the reactions of chlorine atoms with propene and 1-bu-
tene. In contrast to two previous studies, we find no evidence for
large negative temperature dependences of these reactions. The
absence of any discernable effect of temperature on the kinetics
of the reactions in 700–900 Torr at temperatures near ambient is
consistent with expectations based upon the well documented
behavior of the analogous reactions of OH radicals with alkenes
and the reactions of chlorine atoms with ethene and acetylene.
There is no compelling evidence for a large negative temperature
dependences in the reactions of chlorine atoms with unsaturated
organic compounds at temperatures near ambient.
1.0
0.9
0.8
0.7
0.6
0.5
Acknowledgement
0.0024 0.0026 0.0028 0.0030 0.0032 0.0034 0.0036
1 / T(K)
E.W.K. thanks Prof. Craig Donohue and the University of Mich-
igan-Dearborn for invaluable assistance during these experiments.
Figure 5. Comparison of rate constant ratios measured for propene relative to n-
butane as a function of temperature. Solid and dotted lines represent fits to the
current measurements using the GC/FID and FTIR equipment, respectively (see
Figure 1). Also shown are data from the experiments of Caecero-Vega et al. [1]
(diamonds) and Coquet and Ariya [2] (triangles).
References
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been shown to violate simple gas kinetic theory, which dictates
that chemical species cannot react faster than the rate at which
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addition and the rate constants in one atmosphere of air near
ambient temperature display small negative temperature depen-
dencies corresponding to activation energies of ꢀ150 to
ꢀ1000 cal moleꢀ1 [23]. The reaction Cl + C2H2 (kC ) has been
2H2
studied over a wide pressure range at five temperatures spanning
250–370 K [24,25]. The best temperature-dependent expression
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for the high-pressure limiting rate constant [kC = 2.13 ꢂ
2H2
10ꢀ10 (T/300)ꢀ1.045] is non-Arrhenius [24]. However, an Arrhenius
expression with an activation energy of ꢀ650 cal moleꢀ1 also fits
the data well over this temperature range. A combination of exper-
imental data with theoretical interpretation for the Cl + C2H4
reaction [26] yields a value of k1 = 2.96 ꢂ 10ꢀ14
T
1.31 exp(518/
. Again an Arrhenius activation energy of
ꢀ1
T) cm3 moleculeꢀ1
s
Ea = ꢀ250 cal moleꢀ1 can be derived from this non-Arrhenius
expression near ambient temperature.
The simplest explanation for the discrepancy shown in Figure 5
between the temperature dependence of the ratios k1/k3 measured
in our work and those reported by Coquet and Ariya [2] is the pres-
ence of additional (probably heterogeneous) losses of propene at
low temperatures in the study by Coquet and Ariya [2]. This effect
would be similar to the dark reaction observed in our high temper-
ature reactor for 1-butene, which was observed only at ambient
temperature and not higher temperatures (see Section 3.1). As seen
[24] E.W. Kaiser, Int. J. Chem. Kinet. 24 (1992) 179.
[25] E.W. Kaiser, T.J. Wallington, J. Phys. Chem. 100 (1996) 4111.
[26] V.D. Knyazev, I.J. Kalinovski, I.R. Slagle, J. Phys. Chem.
3216.
A 103 (1999)