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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. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 57

The unimolecular decomposition of ethylene oxide (oxirane) and the oxiranyl radial is examined by molecular orbital calculations, Rice-Ramsperger-Kassel-Marcus (RRKM)/Master Equation analysis, and detailed kinetic modeling of ethylene oxide pyrolysis in a single-pulse shock tube. It was found that the largest energy barrier to the decomposition of ethylene oxide lies in its initial isomerization to form acetaldehyde, and in agreement with previous studies, the isomerization was found to proceed through the *CH2CH2O* biradical. Because of the biradical nature of the transition states and intermediate, the energy barriers for the initial C-O rupture in ethylene oxide and the subsequent 1,2-H shift remain highly uncertain. An overall isomerization energy barrier of 59 +/- 2 kcal/mol was found to satisfactorily explain the available single pulse shock tube data. This barrier height is in line with the estimates made from an approximate spin-corrected procedure at the MP4/6-31+G(d) and QCISD(T)/6-31G(d) levels of theory. The dominant channel for the unimolecular decomposition of ethylene oxide was found to form CH3 + HCO at around the ambient pressure. It accounts for >90% of the total rate constant for T > 800 K. The high-pressure limit rate constant for the unimolecular decomposition of ethylene oxide was calculated as k(1,infinity)(s(-1)) = (3.74 x 10(10))T(1.298)e(-29990/T) for 600 < T < 2000 K.