High Accuracy Thermochemical Kinetics for H + CH_3 (+M) ->,<- CH_4 (+M)

摘要

CH_3, the simplest alkyl radical, is an extremely stable intermediate that persists in large concentrations even in high temperature chemically reacting systems such as flames. Radical-radical recombination with H-atoms (R1: H + CH_3 ->,<- CH_4) is the dominant process for CH_3 removal in high temperature combustion and flame processes. Reconciling the disparate experimental databases on k_1 and k_(-1) requires accurate equilibrium constants spanning an extended range of temperatures. In the present work, we include all relevant anharmonic corrections to calculate an accurate Active Thermochemical Tables (ATcT) partition function for CH_3. The resulting nonrigid-rotator-anharmonic-oscillator partition function is used to determine thermochemical parameters (heat capacity, entropy, and enthalpy increment values) for CH_3 and K_(eq) values for reaction R1 over a wide temperature range (200-6000 K). Furthermore, literature experiments and theory (based on two-dimensional master equation calculations with a first principles energy and angular momentum transfer kernel) are used to obtain an accurate representation of the kinetics for k_1(T, P) for use in combustion modeling. Lastly, we assess the impact of incorporating anharmonic thermochemistry for CH_3 and the updated fits for k_1 (and k_(-1)) in current widely used literature models for simulations of CH_4-air laminar flame speeds.