MODELING THE PHOTONUCLEATION OF WATER-VAPOR BY UV IN THE PRESENCE OF OXYGEN AND THE ABSENCE OF POLLUTANTS

The progress on modelling work based on the hypothesis that the photon ucleation of water vapour in the presence of oxygen is due to the form ation of charge-transfer complexes of molecular oxygen and water, H2OO2-, is reported with argument in favour of the relevance of the pheno menon to aerosol formation in the atmosphere. The following results ar e described: (a) potential-energy curves for the complexes H2O . O-2 a nd H2O+O2-, and the calculated cross-section for the UV absorption H2O . O-2 and H2O+O2-; (b) possible alternative photochemical products ar ising from water and oxygen using ab initio electronic structure metho ds; (c) molecular dynamics calculations on small clusters of water mol ecules containing H2O+O2- complexes or H2O2 molecules; (d) an initial estimate of the rate of aerosol formation and of hydrogen peroxide pro duction due to photonucleation in the absence of pollutants.