Thermal decomposition of propyne and allene in shock waves

Abstract Propyne ( p ‐C 3 H 4 ) or allene ( a ‐C 3 H 4 ) mixtures, highly diluted with Ar, were heated to the temperature range 1200–1570 K at pressures of 1.7–2.6 atm behind reflected shock waves. The thermal decompositions of propyne and allene were studied by both measuring the profiles of the IR emission at 3.48 μm or 5.18 μm and analyzing the concentrations of reacted gas mixtures. The mechanism and the rate constant expressions were discussed from both the profiles and the concentrations of reactant and products obtained. The rate constant expressions for reactions, (1) p ‐C 3 H 4 → a ‐C 3 H 4 , (−1) a ‐C 3 H 4 → p ‐C 3 H 4 , and (5) p ‐C 3 H 4 + H → CH 3 + C 2 H 2 were evaluated.