Theoretical interpretation of the kinetics and mechanisms of the HNO + HNO and HNO + 2NO reactions with a unified model

Previously measured decay rates of HNO in the presence of NO have been kinetically modeled on the basis of thermochemical data calculated with the BAC‐MP4 technique. The results of this modeling, aided by TST‐RRKM calculations for the association of HNO and the isomerization, decomposition, and stabilization of the many dimers of HNO, reveal that the decay of HNO under NO‐lean conditions occurs primarily by association forming cis‐ and trans‐(HNO)₂ at temperatures below 420 K. N₂O, which is a relatively minor product, is believed to be formed by H₂O elimination from cis‐HON  NOH, a product of succesive isomerization reactions: trans‐(HNO)₂^† → HN(OH)NO^† → HN(O)NOH^† → cis‐HON NOH^†. The calculated rate constants, which fit experimental data quantitatively, can be represented by k = 10^16.2 × T^−2.40e^−590/T cm³/mol sec for the HNO recombination reaction and k = 10^−2.44T^3.98e^−600/T cm³/mol sec for N₂O formation in the temperature range 80–420 K, at a total pressure of 710 torr H₂ or He. Under NO‐rich conditions, HNO reacts predominantly by the exothermic termolecular reaction, HNO + 2NO → HN(NO)ONO → HN NO + NO₂, with a rate contant of (6 ± 1) × 10⁹ cm⁶/mol² sec at room temperature, based on both HNO decay and NO₂ production. All existing thermal kinetic data on HNO + HNO and HNO + 2NO processes can be satisfactorily rationalized with a unified model based on the thermochemical data obtained by BAC‐MP4 calculations.