Journal of the Mexican Chemical Society
Print version ISSN 1870-249X
IUGA, Cristina; ESQUIVEL OLEA, Rodolfo and VIVIER-BUNGE, Annik. Mechanism and Kinetics of the OH• Radical Reaction with Formaldehyde Bound to an Si(OH)4 Monomer. J. Mex. Chem. Soc [online]. 2008, vol.52, n.1, pp. 36-46. ISSN 1870-249X.
In this work, quantum chemical methods are used to study the reaction of OH· radicals with formaldehyde bound to the Si(OH)4 monomer, as a model for silica mineral aerosols. The potential energy surfaces for the formaldehyde interaction with the surface model have been carefully spanned, and minima and maxima were evaluated. Both the H-abstraction and OH-addition paths are shown to be complex reactions, which involve the formation of a reactant complex in the entrance channel and a product complex in the exit channel. In the main reaction channel, formaldehyde binds to the silanol groups and then reacts with OH free radicals to form a water molecule and a bound formyl radical. We show that the rate constant for the H-abstraction reaction is an order of magnitude smaller when formaldehyde is bound to Si(OH)4 than in the gas phase, while the rate constant for the addition reaction is still about five orders of magnitude smaller. Thus, the branching ratio between abstraction and addition is not significantly altered in the presence of the silicate surface model.
Keywords : Mineral aerosols; radical reactions; silica surface model; formaldehyde; OH radicals; rate constants.