Kinetics of the Reaction between Propargyl Radical and Acetylene

Abstract

The reaction C3H3 + C2H2 → C5H5 (1) has been studied using the Laser Photolysis/Photoionization Mass Spectrometry technique. Rate constants were determined in time-resolved experiments as a function of temperature (800−1100 K). Rate constants of reaction 1 are independent of the bath gas density within the experimental range, [M] = [He] + [C2H2] = (1.2−2.4) × 1017 molecule cm-3. C5H5 was detected as a primary product of reaction 1. Formation of C7H7 was observed with kinetics corresponding to that of a secondary reaction and formation of C9H8 was also observed at even longer reaction times. The kinetics of product formation suggests the following sequence of reactions occurring under the conditions of excess acetylene used in the current work: C3H3 + C2H2 → C5H5 (1), C5H5 + C2H2 → C7H7 (8), and C7H7 + C2H2 → C9H8 + H (9). Within the above experimental range of temperatures and bath gas densities, the rate constants of reaction 1 can be described by the Arrhenius expression k1 = (3.9 ± 1.8) × 10-13 exp(−(...