Energy-structure relationships for microscopic solvation of anions in water clusters

Jaime E. Combariza*, Neil R. Kestner, Joshua Jortner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

219 Scopus citations

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 Møller-Plesset (MP2) level were performed using extended basis sets. Full structural optimization was conducted at the MP2 level for R=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-(H 2O)n (n=2-5), while a "transition" from surface to interior structure may be exhibited for I-(H2O) 6.

Original languageEnglish
Pages (from-to)2851-2864
Number of pages14
JournalThe Journal of Chemical Physics
Volume100
Issue number4
DOIs
StatePublished - 1994

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