Understanding the activation energy trends for the C2H4+OH→C2H4OH reaction by using canonical variational transition state theory
- 8 November 1997
- journal article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 107 (18) , 7266-7274
- https://doi.org/10.1063/1.474967
Abstract
The potential-energy hypersurface of the addition reaction was partially explored following two different approaches. First, the stationary points were located at the MP2(FULL)/6-31G(d,p) level and then the minimum energy path (MEP) was built starting from the MP2 saddle-point geometry. In order to improve the energetics along the MEP, single-point calculations were carried out at several higher levels, in particular, PMP2, MP4sdtq, PMP4sdtq, and QCIsd(t). In a different approach, the C–O bond length was assumed to provide an accurate parametrization of the reaction path in the vicinity of the transition state. The minimum energy structures at the MP4sdq/ level for 16 points along the coordinate have been calculated, followed by a generalized normal-mode analysis at the MP2(FULL)/ level for each point. The initial potential information from both approaches was used to calculate canonical variational transition state (CVT) association rate constants for the temperature range 200–1000 K. Our calculations at the PMP4sdtq/6-311+G(d,p)//MP4sdq/6-311+G(d,p)[MP2(FULL)/6-311 +G(d,p)] level reproduce the inverse dependence of the rate constant with temperature at in agreement with the experimental evidence that this reaction has a negative activation energy at room temperature. The analysis of the enthalpic and entropic contributions to the Gibbs free-energy profile has allowed us to understand those negative values of the activation energy.
Keywords
This publication has 45 references indexed in Scilit:
- Analysis of certain factors in the direct dynamics method: Variational rate constant of the NH3+OH→NH2+H2O reactionThe Journal of Chemical Physics, 1994
- Detailed rate coefficients and the enthalpy change of the equilibrium reaction OH+C2H4=MHOC2H4 over the temperature range 544–673 KThe Journal of Chemical Physics, 1992
- Calculated barrier heights for OH + C2H2 and OH + C2H4 using unrestricted Moeller-Plesset perturbation theory with spin annihilationJournal of the American Chemical Society, 1987
- Ab initio calculations on the barrier height for the hydrogen addition to ethylene and formaldehyde. The importance of spin projectionInternational Journal of Quantum Chemistry, 1986
- Rate constants for the gas–phase reactions of OH radicals with ethylene and halogenated ethylene compoundsThe Journal of Chemical Physics, 1976
- Temperature dependence of the reaction of oxygen atoms with olefinsJournal of the American Chemical Society, 1976
- Relative rate constants for reaction of the hydroxyl radical with a series of alkanes, alkenes, and aromatic hydrocarbonsThe Journal of Physical Chemistry, 1976
- Exact tunneling calculationsJournal of the American Chemical Society, 1971
- A Correlation of Reaction RatesJournal of the American Chemical Society, 1955
- Note on an Approximation Treatment for Many-Electron SystemsPhysical Review B, 1934