Molecular Dynamics Study on the Microscopic Details of the Evaporation of Water

Molecular dynamics simulations were conducted on a drop of water (containing 4890 TIP3P waters) at 350 K. About 70 evaporation events were found and characterized in enough detail to determine significant patterns relating to the mechanism of evaporation. It was found that in almost all evaporation events that a single, high-energy state immediately preceded the evaporation event. In similar to 50% of the cases, this high-energy state involved a short oxygen-oxygen distance, suggesting a van der Waals collision, whereas in the remaining cases, a short hydrogen-hydrogen distance was found, suggesting an electrostatic collision. Of the high-energy states that led to evaporation, about half occurred when the coordination number of water was 1, and about half, when the coordination number was 2. It was found that the 1-coordinated waters (similar to 1% of the surface waters) and 2-coordinated waters (6% of the surface waters) were responsible for almost all the evaporation events.