Water complexes as catalysts in atmospheric reactions

Several atmospherically important reactions involve the formation of a complex between the reagent molecule(s) and one or more water molecules. We will present a brief review of this phenomenon and give some of our recent ab initio results on the effect that the formation of complexes with water may have on the photodissociation of ozone, nitric and peroxynitric acids. Changes in the singlet-triplet potential energy surface splittings and absorption intensities when ozone is complexed with water are inferred from the photochemistry of the complex [Hurwitz and Namaan, 1995]. A significant red shift in the vertical excitation energy of at least one triplet state of ozone is predicted by our calculations, when the molecule is in a complex with water. No such changes are predicted for the acids: their electronic absorption spectra remain unaltered by water complex formation. The infrared absorption intensities of their OH vibrational stretch transitions, however, are enhanced by about an order of magnitude in the complex. (C) 2001 Elsevier Science Ltd. All rights reserved.