Predictive chemical kinetics: Density functional and hartree–fock calculations on free-radial reaction transition states

Density functional theory (DFT ) using gradient-corrected «nonlocal» functionals is used to calculated the thermochemistry and barrier heights for several types of peroxyl radical isomerizations currently being studied by kineticists. The calculations are generally in good agreement with experimental data, where such data are available. An important exception is that the O—H bond strengths in hydroperoxides are all predicted to be too weak by about 7 kcal/mol. The calculated reaction barriers are a few kcal/mol lower than the experimental estimates, but comparable in accuracy to the much more computationally expensive second-order Møller–Plesset (MP 2) predictions. Various theoretical methods converge on a 42 ± 2 kcal/mole barrier for CH₃OO → H₂CO + OH. The DFT calculations can be used to predict reaction barriers in cases where no reliable experimental data are available. The effects of the choice of basis set and correlation functional are explored. Improvements needed to make these calculations most valuable to the chemical kineticist are discussed. © 1994 John Wiley & Sons, Inc.