Kinetics of Phenyl Radical Reactions with Ethane and Neopentane: Reactivity of C 6 H 5 Toward the Primary C-H Bond of Alkanes J. PARK, S. GHEYAS 1 , M. C. LIN Department of Chemistry, Emory University, Atlanta, GA 30322 Received 28 February 2000; accepted 7 August 2000 ABSTRACT: The kinetics of C 6 H 5 reactions with C 2 H 6 (1) and neo-C 5 H 12 (2) have been studied by the pulsed laser photolysis/mass spectrometric method using C 6 H 5 COCH 3 as the phenyl precursor at temperatures between 565 and 1000 K. The rate constants were determined by kinetic modeling of the absolute yields of C 6 H 6 at each temperature. Another major product, C 6 H 5 CH 3 , formed by the recombination of C 6 H 5 and CH 3 , could also be quantitatively modeled using the known rate constant for the reaction. A weighted least-squares analysis of the two sets of data gave k 1 = 10 11.320.05 exp[-(2236  91)/T] cm 3 mol -1 s -1 and k 2 = 10 11.370.03 exp[-(1925  48)/T] cm 3 mol -1 s -1 for the temperature range studied. The result of our sen- sitivity analysis clearly supports that the yields of C 6 H 6 and C 6 H 5 CH 3 depend primarily on the abstraction reactions and C 6 H 5 + CH 3 , respectively. From the absolute rate constants for the two reactions we obtained the value for the H-abstraction from a primary C-H bond, k p -CH = 10 10.400.06 exp(-1790  102/T) cm 3 mol -1 s -1 . This result is utilized for analysis of other kinetic data measured for C 6 H 5 reactions with alkanes in solution as well as in the gas phase.  2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 64–69, 2001 INTRODUCTION In general, phenyl radical is more reactive than alkyl radicals [1], but unlike the alkyl, there has been very little information available on the reactivity of C 6 H 5 towardaspecifictypeofC-Hbondsofalkanesinthe gas phase; namely, the primary, secondary, and terti- aryCHbonds. There had been many relative rate measurements Correspondence to: M. C. Lin (chemmcl@emory.edu) Contract grant sponsor: Basic Energy Sciences, Department of Energy Contract grant number: DE-FG02-97-ER14784 1 Current address: Chemistry Department, Temple University, Philadelphia, PA 19122  2000JohnWiley&Sons,Inc. forphenylreactionsinsolutionbyBridgerandRussell using C 6 H 5 + CCl 4 asareferencestandard[2].From a series of studies carried out at 333 K, they deter- minedtherelativereactivitiesofC 6 H 5 towardthepri- mary, secondary, and tertiary C-H bonds (0.12  0.01):1.01:4.8 for aliphatic hydrocarbons larger than C 4 . Further discussion on this and other relative rate datawillbemadelateronthebasisofournewresults fortheprimaryC-Hreactionandthoseforsecondary and tertiary C-H reactions reported previously [3,4]. Thisstudyisacontinuationofourinvestigationon thekineticsofC 6 H 5 radicalreactions[3–9]employing thecavityringdownspectrometry(CRDS)[10]and/or the pulsed laser photolysis/mass spectrometry (PLP/ MS)[11].Forseveralsystemsinvestigated,additional