Modelling the photonucleation of water vapour by UV in the presence of oxygen and the absence of pollutants

The progress on modelling work based on the hypothesis that the photonucleation of water vapour in the presence of oxygen is due to the formation of charge-transfer complexes of molecular oxygen and water, H2O+O2-, is reported with argument in favour of the relevance of the phenomenon to aerosol formation in the atmosphere. The following results are described: (a) potential-energy curves for the complexes H2O·O2 and H2O+O2-, and the calculated cross-section for the UV absorption H2O·O2 → H2O+O2-; (b) possible alternative photochemical products arising from water and oxygen using ab initio electronic structure methods; (c) molecular dynamics calculations on small clusters of water molecules containing H2O+O2- complexes or H2O2 molecules; (d) an initial estimate of the rate of aerosol formation and of hydrogen peroxide production due to photonucleation in the absence of pollutants.