Master equation modeling of wide range temperature and pressure dependence of CO + OH → products

The rate coefficient of CO + OH → products is analyzed with RRKM/master equation analyses and Monte Carlo simulations. The analyses are based on the recent CCSD(T)/cc‐pvTZ potential energy surface of Yu et al. Chem Phys Lett 2001, 349, 547–554). It is shown that the experimental data over the temperature range of 80–2500 K and pressure from 1 Torr to 800 bar can be satisfactorily reproduced by lowering the CCSD(T)/cc‐pvTZ energy barrier for the CO 2 + H exit channel by 1 kcal/mol and more importantly, by considering an equilibrium factor in the thermal rate constant formulation. This factor accounts for the populations of rovibrationally excited trans ‐ and cis ‐HOCO, which are then allowed to dissociate only through specific paths that are open to them. By modeling the isothermal but pressure‐dependent rate data of Fulle et al. ( J Chem Phys 1996, 105, 983–1000) over the temperature range from 98 to 819 K, we obtained an 〈 E down 〉 value equal to 150 cm −1 for M = He. The 〈 E down 〉 values for M = N 2 , Ar, CF 4 , and SF 6 were also obtained by fitting the OH and OD data at 298 K. Based on the theoretical analyses, we recommended that the following rate expression be used for CO + OH → CO 2 + H in the temperature range from 120 to 2500 K and pressure lower than P (bar) = 9 × 10 −17 T 5.9 exp(520/ T ): k 1b,0 (cm 3 molecule −1 s −1 ) =1.17 × 10 −19 T 2.053 exp(139/ T ) + 9.56 × 10 −12 T −0.664 exp(−167/ T ). Fall‐off parameterization is also proposed for the rate coefficient of CO + OH → CO 2 + H under extremely high pressures and for CO + OH → HOCO over the temperature range from 120 to 2500 K.