The temperature dependence of absolute rate constants for the F+H2 and F+D2 reactions

Abstract

Multiphoton dissociation of SF6 has been used to generate a transient concentration of fluorine atoms in mixtures with argon and H2 or D2. Absolute rate constants for the F+H2 and F+D2 reactions have been determined as a function of temperature by monitoring the appearance rate of HF or DF product chemiluminescence. In the temperature range from 190 °K to 373 °K the results are fit by the expressions kH=1.0×10−10 exp(−(860±100)/RT) and kD=9.1×10−11 exp(−(1100±100)/RT), both in cm3 molecule−1 sec−1. These values are in rough agreement with those obtained recently using a similar technique. The value of the isotope effect kH/kD is in good agreement with two previously determined values.

The kinetics of the reaction F + H2 ? HF + H. A critical review of literature data

“…The error limits reported by Zhitneva and Pshezhetskii are Ϯ 17%, but it seems that the inaccuracy is much larger. Table I also includes the results of Bozzelli [8], which are in good agreement with the results of Wurzberg and Houston [5], Stevens et al [6], and the results of the two studies of Clyne et al [9,11]. The details of the experiments of Bozzelli are not known to us, because they were summarized in a Ph.D. thesis not available to us.…”

“…It should be noted that values of the kinetic isotope effect k FϩH 2 /k FϩD 2 , calculated from the average values of k FϩH 2 and k FϩD 2 from these two groups [5,6], are in good agreement with those obtained by the competitive methods [15,16], with differences of less than 10% over the whole temperature range.…”

“…The isotope effect calculated from their results is practically independent of temperature, which means that the activation energy for both reactions, F ϩ H 2 and F ϩ D 2 , is approximately the same. In contrast to this behavior, the results of Wurzberg and Houston [5] and of Stevens et al [6] exhibit normal behavior: the kinetic isotope effect decreases with increasing temperature. The activation energy differences, Ea(F ϩ D 2 ) Ϫ Ea(F ϩ H 2 ), obtained by these two groups are 240 cal/mol and 420 cal/mol, respectively.…”

“…In view of the above discussion concerning the kinetic isotope effect and also taking into consideration the temperature ranges of the experiments, it seems to us that the preferred Arrhenius expression for k FϩH 2 , which should also cover temperatures significantly below room temperature, should be based mainly on the results of Wurzberg and Houston [5] and of Stevens et al [6]. We therefore recommend for the temperature range 190 -376 K the following Arrhenius expression,…”

Dynamic Resonances in the Reaction of Fluorine Atoms with Hydrogen Molecules

“…This discrepancy, as well as other recent developments (15, [29][30], suggest that the M5 surface is an inadequate representation of the F + H2 potential energy surface.…”