Reactions between the OH. radical and oxygen-containing atmospheric pollutants:: a theoretical description

The potential energy surface of the reacting system OH + O.P., where the oxygenated pollutant O.P. is H2CO, H3COH, H3COCH3 and H2CCH2O, has been investigated at different levels of theory using either the 6-31G* or the 6-311G** basis set. Various DFT functionals also have been tested. Activation energies and reaction enthalpies have been estimated. The results show that: (i) a satisfactory agreement with the available experimental data (activation energies) can be obtained using traditional correlated methods such as the QCISD method with the 6-311G** basis; (ii) reasonable results are also obtained at the MP2/6-311G** level; and (iii) the geometrical parameters computed with the 6-31G* basis agree fairly well with those provided by the more extended 6-311G** basis. Finally, our results point out the inadequacy of the DFT approach, based on the most popular functionals available in the literature (B3LYP, B3PW91, BLYP), to describe this kind of reaction characterized by polar transition states. (C) 2001 Elsevier Science B.V. All rights reserved.