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

TLDR: In this article, the authors analyzed the rate coefficient of CO+OH products with RRKM/master equation analyses and Monte Carlo simulations and showed 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 CO2+H exit channel by 1 kcal/mol and more importantly, by considering an equilibrium factor in the thermal rate constant formulation.

Abstract: 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 CO2 + 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 〈Edown〉 value equal to 150 cm−1 for M = He. The 〈Edown〉 values for M = N2, Ar, CF4, and SF6 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  CO2 + H in the temperature range from 120 to 2500 K and pressure lower than P(bar) = 9 × 10−17T5.9 exp(520/T): k1b,0(cm3 molecule−1s−1) =1.17 × 10−19T2.053exp(139/T) + 9.56 × 10−12T−0.664 exp(−167/T). Fall-off parameterization is also proposed for the rate coefficient of CO + OH  CO2 + H under extremely high pressures and for CO + OH  HOCO over the temperature range from 120 to 2500 K. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38:57–73, 2006