Water Dimers in the Atmosphere: Equilibrium Constant for Water Dimerization from the VRT(ASP-W) Potential Surface

The equilibrium constant for water dimerization ( K P ) was determined as a function of temperature via rigorous calculation of the canonical (H 2 O) 2 partition function using the recently developed split Wigner pseudo-spectral method and the VRT(ASP-W) pair potential. Our K P (T) values are significantly larger than those from previous theoretical treatments but somewhat smaller than literature experimental values, which exist, however, only over a very limited temperature range. These results indicate that water dimers can exist in sufficient concentrations (e.g., 10 16 cm -3 at 40 °C and 100% relative humidity) to affect physical and chemical processes in the atmosphere.