Ab initio investigation of the structure, stability, and atmospheric distribution of molecular clusters containing H2O, CO2, and N2O

Abstract

We present results from ab initio calculations for the structures and energetic properties of neutral clusters containing water, carbon dioxide, and nitrous oxide using the complete basis set CBS-Q multilevel procedure. Gas phase hydration energies ΔG0, enthalpies ΔH0, and entropies ΔS0 for the stepwise attachment of water onto clusters according to X·(H2O)n + H2O ↔ X·(H2O)n+1 (X = CO2, N 2O, and H2O) are reported for n ≤ 4. In particular, our results demonstrate that values for the incremental hydration enthalpies and entropies of all three gases CO2, N2O, and H2O asymptotically approach values characteristic of bulk water (i.e., -44.0 kJ mol-1 for the enthalpy and - 118.8 J K-1 mol-1 for the entropy of condensation) following attachment of around three to four water molecules. Our ab initio calculations indicate that water attachment onto CO2, N2O, and H2O is a thermodynamically favorable process, such that hydrated CO2·(H 2O)n, N2O(H2O)n, and H2O(H2O)n clusters would form a significant atmospheric repository of these species. Copyright 2008 by the American Geophysical Union.