Kinetics and products of propargyl (C3H3) radical self- reactions and propargyl-methyl cross-combination reactions

Propargyl (HC=C-CH2) and methyl radicals were produced through the 193-nm e xcimer laser photolysis of mixtures of C3H3Cl/He and CH3N2CH3/He, respectiv ely. Gas chromatographic and mass spectrometric (GC/MS) product analyses we re employed to characterize and quantify the major reaction products. The r ate constants for propargyl radical self-reactions and propargyl-methyl cro ss-combination reactions were determined through kinetic modeling and compa rative rate determination methods. The major product of the propargyl radic al combination reaction at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C6H6 isomers with 1,5-hexadiyne(CH=C-CH2- CH2-C=CH, about 60%); 1,2-hexadiene-5yne (CH2=C=C-CH2-C=CH, about 25%); and a third isomer of C2H6 (similar to 15%), which has not yet been, with cert ainty, identified as being the major products. The rate constant determinat ion in the propargyl-methyl mixed radical system yielded a value of (4.0 +/ - 0.4) X 10(-11) cm(3) molecule(-1) s(-1) for propargyl radical combination reactions and a rate constant of (1.5 +/- 0.3) X 10(-10) cm(3) molecule(-1 )s(-1) for propargyl-methyl cross-combination reactions. The products of th e methyl-propargyl cross-combination reactions were two isomers of C4H6, 1- butyne (about 60%) and 1,2-butadiene (about 40%). (C) 2000 John Wiley & Son s. Inc.