Neutral water clusters in the Earth’s atmosphere: The effect of orientational isomerism on their concentrations and thermodynamic parameters.

In order to estimate the effect of orientational isomerism on the thermodynamic parameters and concentrations of water clusters in the gas phase, all possible structures of book, cageand prismconformations of water hexamer (H2O)6have been studied using the DFT (B3LYP/6-311++G(2d,2p)), G4, DFTB, W1BD and MB-pol calculations. It was found that taking into account of the orientational isomerism leads to the values of water cluster gas-phase concentrations different by 1–2 orders of magnitude from the results obtained when only single or several most energetically favorable structures are considered. The concentrations of all the considered hexamer structuresin the saturated water vapor at T= 298.15 K are estimated as 1.61 103(G4) and 8.17 105 (DFT) molecules/cm3.