Thermodynamic properties of forming methanol-water and ethanol-water clusters at various temperatures and pressures and implications for atmospheric chemistry: A DFT study

The gas-phase geometries, binding energies, enthalpies, and free energies of methanol - (water)(n) and ethanol - (water)(n) clusters containing n = 1 - 10, 20, 30, 40, and 50 water molecules have been calculated using density functional theory. The binding energies are calculated at 0 K. The enthalpies are calculated at a temperature of 298.15 K and pressure of 1013.25 hPa (1 atm). The free energies are calculated at a wide range of temperature (T) and pressure (P) (from T = 298.15 K, P = 1013.25 hPa to T = 216.65 K, P = 226.32 hPa). The results show that the free energy of the formation of a specific cluster from its free molecules is negative (i.e., favorable) only below some critical temperature and pressure, which depends on the cluster's size. One of the most common volatile organic compounds (VOCs) in the troposphere is methanol, ethanol, and atmospheric aerosols containing methanol and ethanol. The Rayleigh scattering properties of methanol-water and ethanol-water clusters have been investigated. The scattering intensities were computed at static (8 nm) and different wavelengths (700, 600, 500, and 400 nm) of naturally polarized light. Rayleigh scattering intensities increase about 9%-10% at 400 nm compared to the static limit (8 nm) for both methanol-water and ethanol-water clusters. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Gas-phase properties of methanol-water and ethanol-water clusters were calculated using density functional theory, revealing that the free energy of specific clusters is negative only at certain temperature and pressure conditions. The Rayleigh scattering properties of these clusters were investigated and an increase in scattering intensity was observed at 400 nm compared to the static limit.