C2D5I dissociation and D+CH3→CH2D+H at high temperature:: Implications to the high-pressure rate constant for CH4 dissociation

The shock tube technique with H- and D-atom atomic resonance absorption spectrometry detection has been used to study the thermal decomposition Of C2D5I and the reaction, (1) CH3 + D --> CH2D + H over the temperature ranges 924-1370 and 1294-1753 K, respectively. First-order rate constants for the thermal decomposition of C2D5I can be expressed by the Arrhenius equation, logk(C2D5I) = (10.397 +/- 0.297) - (7700 +/- 334 K)/T, giving k(C2D5I) = 2.49 X 10(10) exp(-17,729 K/T) s(-1). The branching ratio between product channels, C2D5 + I and C2D4 + DI, was also determined. These results coupled with the fast decomposition of C2D5 radicals were then used to specify [D](t) in subsequent kinetics experiments with CH3 where [CH3](0) was prepared from the concurrent thermal decomposition of CH3I. Within experimental error, the rate constants for reaction I were found to be temperature independent with k(1) = (2.20 +/- 0.22) X 10(-10) cm(3) molecule(-1) s(-1). The present data have been combined with earlier lower temperature determinations and the joint database has been examined with unimolecular rate theory The implications of the present study can be generalized to supply a reliable value for the high-pressure limiting rate constant for methane dissociation.