Size evolution of the equilibrium structures of ArnH 2O van der Waals clusters with n=1-14 has been investigated. Pairwise additive jntermolecular potential energy surfaces (IPESs) for Ar 2H2O clusters were constructed from the spectroscopically accurate Ar-Ar and anisotropic 3D Ar-H2O potentials. For each cluster size considered, we determined the global minimum of the respective IPES and several other lowest-lying ArnH2O isomeric structures. This was accomplished by using simulated annealing followed by a direct minimization scheme. The minimum-energy structures of all ArnH 2O clusters considered in this work are fully solvated; up to n=12, the Ar atoms fill a monolayer around H2O. For n=12, the optimal Ar12H2O structure has the Ar atoms arranged in a highly symmetrical icosahedron, with H2O in its center. The icosahedral Ar12H2O structure is exceptionally stable; the energy gap separating it from the next higher n=12 isomer (289.55 cm-1) exceeds that for any other cluster in this size range. The observed preference for solvated ArnH2O structures was carefully analyzed in terms of the relative energetic contributions from Ar-Ar and Ar-H2O interactions. For n≤9, the monolayer, cagelike geometries are favored primarily by providing optimal Ar-H2O interactions, significantly larger than for alternative ArnH2O structures. For n>9, the solvated ArnH2O isomers offer the best Ar-Ar packing, in addition to the strongest total Ar-H2O interactions. A detailed comparison was made with the minimum-energy structures of ArnHF clusters, determined by us recently [J. Chem. Phys. 100, 7166 (1994)], revealing interesting differences in the growth patterns of the optimal cluster structures.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry