Shock tube/laser absorption measurements of the isomerization rates of allene and propyne

Abstract

Two novel laser absorption diagnostics for allene and propyne are presented. Through examination of the high temperature spectra of the two C3H4 isomers via two fast-wavelength-scanning, broadband external cavity quantum cascade lasers, 1930.38 cm−1 and 1233.3 cm−1 were chosen as the wavelengths for a two-species, two-wavelength diagnostic pair that minimizes interference from other species. Absorption cross sections for allene and propyne were measured at each of these wavelengths over 1196–1502 K, at 1.3–1.6 atm. Once characterized, these diagnostics were employed to measure the mutual isomerization rates of allene and propyne over the same temperature range. The two rates are reported as kA->P (1202–1502 K) = 2.64 × 1012exp(-59,214/RT) ±14% and kP->A (1196–1494 K) = (4.19 × 1012)exp(-61,912/RT) ±17%. These rates were found to be in excellent agreement with limited past experimental determinations and recently computed rates. Using these rates, the equilibrium constant is also reported as a function of temperature.