CH2CH2Cl a C2H4 + Cl Reaction
J. Phys. Chem. A, Vol. 103, No. 17, 1999 3221
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are Fcent(He) ) 0.467 and Fcent(N2) ) 0.505 (independent of
temperature). The average deviation of fit is 8% and maximum
deviation is 19%. The upper temperature limit of the rate
constant parametrization is determined by the significance of
non-steady-state effects39,40 above 800 K where the notion of a
time-independent rate constant is inapplicable.
This parametrization is most reliable under the conditions of
the experiments on the results on which the model of reaction
1,-1 was based, that is, room temperature for the predicted
k-1 values and T ) 400-480 K and low pressures for k1. One
should bear in mind that the above model of the reaction is
based on significant simplifications and that the available
experimental data are not sufficient to specify all the parameters
of even the simplified model. In particular, different temperature
dependencies of the collisional parameters and a different (within
uncertainties) heat of formation of CH2CH2Cl will result in
different values of rate constants. Moreover, the simplifications
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and the representation of the tumbling motion of the C2H4
fragment relative to the Cl atom in the transition state with low-
frequency vibrational modes) result in uncertainties which are
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Acknowledgment. This research was supported by the
National Science Foundation, Division of Chemical, Biochemi-
cal and Thermal Engineering under Grant CTS-9311848. The
authors thank Drs. E. W. Kaiser and T. J. Wallington for sharing
their experimental data.
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Supporting Information Available: Supplement describing
the results of the ab initio study of reaction (1,-1) (four pages).
Table 1S containing information on the properties of several
conformations on the potential energy surface. Figure 1S
describing potential energy surface scans. Supporting Informa-
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