Water Dimers in the Atmosphere III: Equilibrium Constant from a Flexible Potential

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 110; no. 16; pp. 5411 - 5419
• Main Authors: Scribano, Yohann, Goldman, Nir, Saykally, R. J, Leforestier, Claude
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 27.04.2006
• Subjects: Atomic and Molecular Clusters; Physics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp056759k

We present new results for the water dimer equilibrium constant K p(T) in the range 190−390 K, using a flexible potential energy surface fitted to spectroscopical data. The increased numerical complexity due to explicit consideration of the monomer vibrations is handled via an adiabatic (6 + 6)d decoupling between intra- and intermolecular modes. The convergence of the canonical partition function of the dimer is ensured by computing all energy levels up to dissociation for total angular momentum values J = 0−5 and using an extrapolation scheme to higher values. The newly calculated values for K p(T) are in very good agreement with available experimental data at room temperature. At higher temperatures, an analysis of the convergence of the partition function reveals that quasi-bound states are likely to contribute to the equilibrium constant. Additional thermodynamical quantities (ΔG, ΔH, ΔS, and C p) have also been determined and fit to quadratic expressions a + bT + cT 2.