Rate coefficients for fuel + NO2: Predictive kinetics for HONO and HNO2 formation

Abstract

High-accuracy electronic structure calculations and transition state theory are used to predict the rate coefficients for the H-abstraction reactions H2+NO2 and CH4+NO2. In each case, three different HNO2 isomers are formed: cis-HONO, trans-HONO, and HNO2. These results are used as benchmarks to test different combinations of density functionals and basis sets. The performance of these DFT methods are evaluated both with and without the use of subsequent CCSD(T)-F12a single-point energy corrections. The compound method CCSD(T)-F12a/cc-pVTZ-f12//B2PLYPD3/cc-pVTZ is used to predict the rate coefficients for C2–C4 alkanes and alkenes+NO2, and the resulting activation energies are generalized into rate rules. These new rules will enable accurate rate coefficients for RH+NO2 reactions for larger hydrocarbons. In all cases, the dominant product for RH+NO2 is R+cis-HONO, followed by R+HNO2. Although trans-HONO is the most stable HNO2 isomer, the rate constants leading to its formation are roughly an order of magnitude smaller.