1National Space Institute, Technical University of Denmark, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
2Department of Chemistry, H.C. Ørsted Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark
3Division of Atmospheric Sciences and Geophysics, Dept. of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
Received: 17 Mar 2011 – Discussion started: 06 May 2011
Abstract. An ab initio study of gaseous clusters of O2− and O3− with water is presented. Based on thorough scans of configurational space, we determine the thermodynamics of cluster growth. The results are in good agreement with benchmark computational methods and existing experimental data. We find that anionic O2−(H2O)n and O3−(H2O)n clusters are thermally stabilized at typical atmospheric conditions for at least n = 5. The first 4 water molecules are strongly bound to the anion due to delocalization of the excess charge while stabilization of more than 4 H2O is due to normal hydrogen bonding. Although clustering up to 12 H2O, we find that the O2 and O3 anions retain at least ca. 80 % of the charge and are located at the surface of the cluster. The O2− and O3− speicies are thus accessible for further reactions. We consider the distributions of cluster sizes as function of altitude before finally, the thermodynamics of a few relevant cluster reactions are considered.
Revised: 12 Jul 2011 – Accepted: 13 Jul 2011 – Published: 21 Jul 2011
Bork, N., Kurtén, T., Enghoff, M. B., Pedersen, J. O. P., Mikkelsen, K. V., and Svensmark, H.: Ab initio studies of O2−(H2O)n and O3−(H2O)n anionic molecular clusters, n≤12, Atmos. Chem. Phys., 11, 7133-7142, doi:10.5194/acp-11-7133-2011, 2011.