| Abstract
| - The reflected shock tube technique with D atom atomic resonance absorption spectrometry (ARAS) detectionhas been used to study the bimolecular reaction, D + C2H2 → C2HD + H. D atoms were produced from thethermal decomposition of C2D5I above ∼1150 K. The initially formed C2D5 radicals rapidly decompose togive D + C2D4. Rate constant values were obtained from both reactant and product hydrogen atommeasurements, and these were found to be identical within experimental error. The title reaction proceedsthrough a vibrationally excited vinyl radical, and the equivalence of results based on reactant and productmeasurements suggests that radical stabilization is negligible over the temperature and pressure ranges of theexperiments. For 1100 ≤ T ≤ 1630 K, the results can be described by the linear-least-squares Arrheniusexpression: k = (2.77 ± 0.45) × 10-10 exp(−3051 ± 210 K/T) in units of cm3 molecule-1 s-1, with the onestandard deviation of the values from the equation being ±10.7%. Application of RRKM theory with negligiblestabilization shows that k = kD∞〈kfε/(kfε+ kbε)〉 where the kiε's refer to RRKM evaluated specific rate constantsfor forward and backward dissociations, and kD∞ is the high-pressure limiting rate constant for D addition toacetylene. Hence, the present measurements coupled with earlier measurements and modern ab initio potentialenergy determinations allow for specification of the high-pressure limiting rate constants. The same modelcan then be used for the protonated reaction, H + C2H2, where a considerable ambiguity has existed forabout 30 years.
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