C{sub 2}D{sub 5}I dissociation and D + CH{sub 3} {yields} CH{sub 2}D + H at high temperature : implications to the high pressure rate constant for CH{sub 4} dissociation.

The shock tube technique with H- and D-atom atomic resonance absorption spectrometry (ARAS) detection has been used to study the thermal decomposition of C{sub 2}D{sub 5}I and the reaction, CH{sub 3} + D'' CH{sub 2}D + H, (1) over the temperature ranges, 924-1370 K and 1294-1753 K, respectively. First-order rate constants for the thermal decomposition of C{sub 2}D{sub 5}I can be expressed by the Arrhenius equation, logk{sub C2D5I} = (10.397 {+-} 0.297) - (7700 {+-} 334 K)/T, giving k{sub C2D5I} = 2.49 x 10{sup 10} exp(-17729 K/T) s{sup -1}. The branching ratio between product channels, C{sub 2}D{sub 5} + I and C{sub 2}D{sub 4} + DI, was also determined. These results coupled with the fast decomposition of C{sub 2}D{sub 5} radicals were then used to specify [D]{sub t} in subsequent kinetics experiments with CH{sub 3} where [CH{sub 3}]{sub 0} was prepared from the concurrent thermal decomposition of CH{sub 3}I. Within experimental error, the rate constants for reaction (1) were found to be temperature independent with k{sub 1} = (2.20 {+-} 0.22) x 10{sup -10} cm{sup 3} molecule{sup -1} s{sup -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