1. Energy-structure relationships for microscopic solvation of anions in water clusters.
- Author
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Combariza, Jaime E., Kestner, Neil R., and Jortner, Joshua
- Subjects
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SOLVATION , *ANIONS , *WATER , *FORCE & energy - Abstract
In this paper we present a quantum-mechanical study of anions in water clusters, X-(H2O)n (X=Cl, Br, I, and n=1–6). Molecular orbital calculations at the self-consistent field (SCF) level and at the second-order Mo\ller–Plesset (MP2) level were performed using extended basis sets. Full structural optimization was conducted at the MP2 level for n=1 and at the SCF level for n=2–6. The energies and charge distribution of X-(H2O) were calculated at the MP2 level, while the energies of the X-(H2O)n (n=2–6) clusters were calculated at the MP2 level using the SCF optimized geometry. Calculations of total and sequential enthalpies of hydration and for the vertical ionization potentials were conducted for X-(H2O), the hydrogen bonded and linear isomers of X-(H2O)2, the pyramidal structure of X-(H2O)3, and the interior and surface isomers of X-(H2O)n, n=4–6. The calculated hydration enthalpies account well for their experimental size dependence for n=1–6. However, the isomer specificity of the hydration enthalpies is reflected by a small energy difference (δ=1–5 kcal mol-1) between the surface and interior isomers at a fixed n, precluding the assignment of structural isomers on the basis of ground-state energetics. The cluster size dependence and isomer specificity of the calculated vertical ionization potentials in conjunction with experimental data provide a diagnostic tool for the structural assignment of isomers and for the distinction between surface and interior structures. The central prediction emerging from the structure-energetic relations based on cluster size dependence and isomer specificity of vertical ionization potentials, is the prevalence of surface structures for Cl-(H2O)n (n=2–6), Br-(H2O)n (n=2–6), and I-(H2O)n (n=2–5), while a ‘‘transition’’ from surface to interior structure may be exhibited for I-(H2O)6. [ABSTRACT FROM AUTHOR]
- Published
- 1994
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