Thermal rate constants of the pyrolysis of n-Heptane

Abstract

Rate coefficients for straight chain alkane and free radical decomposition are important in combustion process. This work reports a theoretical study of the pyrolysis of n-Heptane. The barrier heights of the C−C fission reaction, β-scission reaction and H-atom abstraction reaction, as well as geometrical parameters of the reactants, products, and transition states involved in the decomposition of n-Heptane have been calculated at the CCSD(T)/6–311G( d,p)//B3LYP/6–311G( d,p) level. The temperature-dependent rate constants for individual reaction have been obtained in the temperature range of 200–3000 K using variational transition state theory and Rice–Ramsperger–Kassel–Marcus theory. The pressure dependence rate constants have been treated by one-dimensional master equation calculations at different pressure as well as high-pressure limit. In order to facilitate the use of the reaction rate constants for chemical kinetics modeling, all of the individual rate constants were fitted to a modified three-parameter Arrhenius expression: k( T) = AT n exp(− E b / RT) at various pressures. Some of the predicted rate constants are in reasonable agreement with the available experimental and previous theoretical results. The pyrolysis mechanism and RRKM-based rate constants presented in this paper may be used in high accuracy combustion modeling.