Water Dimers in the Atmosphere II: Results from the VRT(ASP-W)III Potential Surface

We report refined results for the equilibrium constant for water dimerization ( K P ), computed as a function of temperature via fully coupled 6D calculation of the canonical (H 2 O) 2 partition function on VRT(ASP-W)III, the most accurate water dimer potential energy surface currently available. Partial pressure isotherms calculated for a range of temperatures and relative humidities indicate that water dimers can exist in sufficient concentrations (e.g., 10 18 m -3 at 30 °C and 100% relative humidity) to affect physical and chemical processes in the atmosphere. The determinations of additional thermodynamic properties (Δ G, Δ H, Δ S, C P, and C V ) for (H 2 O) 2 are presented, and the role of quasi-bound states in the calculation of K P is discussed at length.