Water complexes as catalysts in atmospheric reactions

Several atmospherically important reactions involve the formation of a comp lex between the reagent molecule(s) and one or more water molecules. We wil l 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. Cha nges in the singlet-triplet potential energy surface splittings and absorpt ion intensities when ozone is complexed with water are inferred from the ph otochemistry of the complex [Hurwitz and Namaan, 1995]. A significant red s hift in the vertical excitation energy of at least one triplet state of ozo ne is predicted by our calculations, when the molecule is in a complex with water. No such changes are predicted for the acids: their electronic absor ption spectra remain unaltered by water complex formation. The infrared abs orption intensities of their OH vibrational stretch transitions, however, a re enhanced by about an order of magnitude in the complex. (C) 2001 Elsevie r Science Ltd. All rights reserved.