HR: 1340h
AN: A13A-0883    [Abstracts]
TI: Ab Initio Investigation of the Structure, Stability and Atmospheric Distribution of Molecular Clusters Containing H2O, CO2 and N2O.
AU: * Lemke, K H
EM: kono@erdw.ethz.ch
AF: ETH Zurich, Institute for Mineralogy and Petrology, Zurich, 8006, Switzerland
AU: Seward, T M
EM: tseward@erdw.ethz.ch
AF: ETH Zurich, Institute for Mineralogy and Petrology, Zurich, 8006, Switzerland
AB: We present results from ab initio calculations for the structures, energetics and atmospheric abundances of neutral clusters containing water, carbon dioxide and nitrous oxide up to 45km altitude using the complete basis set CBS-Q and G3 multi-level procedures. Gas phase hydration energies, enthalpies and entropies for the stepwise attachment of water onto clusters according to X(H₂O)_n + H₂O = X(H₂O)_n+1 (where X = H₂O, CO₂ and N₂O) are reported for up to n=5. In particular, our results demonstrate that values for the incremental hydration enthalpies and entropies of all three gases H₂O, CO₂ and N₂O asymptotically approach values characteristic of bulk liquid water (i.e. -44.0 kJ/mol for the enthalpy and -118.8 J/Kmol for the entropy of condensation) following attachment of around 3-4 water molecules. Interestingly, our calculated number densities for the water dimer at 292Kelvin are in excellent agreement with recent values obtained from IR measurements of atmospheric media (Pfeilsticker et al., 2003, Science). Our quantum chemical calculations indicate that water attachment onto H₂O, CO₂ and N₂O is a thermodynamically favorable process, such that hydrated clusters would form a significant atmospheric repository of these species.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0340 Middle atmosphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting