Falloff behavior in propane thermal decomposition at high temperature

The falloff from the high-pressure limiting unimolecular rate constant for propane thermal dissociation at temperatures in the range from 1300 to 1700 K and densities near 1.5 ×10^-5 mol/cm³ was investigated experimentally and analytically. The experiments were done in reflected shock waves in 5% mixtures of propane in argon and in nitrogen by IR laser kinetic absorption spectroscopy. Computer modeling was used to determine the rate constant for the primary decomposition step and to define the sensitivity of the experiments to values of rate constants and absorptivities. The rate constant expression deduced for the decomposition reaction appeared to decrease by factors between 3 and 10 from the high-pressure limiting value, in accord with RRK models.