Kinetics and products of propargyl (C 3 H 3 ) radical self‐reactions and propargyl‐methyl cross‐combination reactions

Propargyl (HCCCH 2 ) and methyl radicals were produced through the 193‐nm excimer laser photolysis of mixtures of C 3 H 3 Cl/He and CH 3 N 2 CH 3 /He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self‐reactions and propargyl‐methyl cross‐combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C 6 H 6 isomers with 1,5‐hexadiyne(CHCCH 2 CH 2 CCH, about 60%); 1,2‐hexadiene‐5yne (CH 2 CCCH 2 CCH, about 25%); and a third isomer of C 6 H 6 (∼15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl‐methyl mixed radical system yielded a value of (4.0 ± 0.4) × 10 −11 cm 3 molecule −1 s −1 for propargyl radical combination reactions and a rate constant of (1.5 ± 0.3) × 10 −10 cm 3 molecule −1 s −1 for propargyl‐methyl cross‐combination reactions. The products of the methyl‐propargyl cross‐combination reactions were two isomers of C 4 H 6 , 1‐butyne (about 60%) and 1,2‐butadiene (about 40%). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 118–124, 2000