Accurate rate expressions for simulations of gas-phase chemical reactions

Several of the commonly used expressions giving reaction rates for model chemical reactions, though accurate for very high activation energies (i.e. E_a ≫ k_BT), are inaccurate for more typical reaction conditions. In this paper we provide the complete and accurate rate expressions for model reactions having cross-sections dependent on translational, line-of-centers translational, and internal energies as well as on combinations thereof. Included are rate expressions for models giving Arrhenius-like temperature dependencies. Tests of several of the models and their corresponding cross-section expressions were made using Bird's direct simulation Monte Carlo method. These were successful in reproducing the experimentally determined rates over the full range of temperatures for the representative reactions: HF + H → H₂ + F, CO + OH → CO₂ + H, H₂ + O → OH + H and H₂ + Cl → HCl + H.