Water evaporation: a transition path sampling study.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Statistical Mechanics

Background:

• Understanding liquid evaporation is crucial for various thermodynamic and transport processes.
• Previous studies have explored water evaporation using molecular dynamics, but detailed characterization of the transition state remains challenging.

Purpose of the Study:

• To investigate the molecular mechanisms of water evaporation using transition path sampling.
• To characterize the transition state ensemble (TSE) and the dynamics of evaporating water molecules.

Main Methods:

• Employed transition path sampling (TPS) to generate thousands of evaporation trajectories for the SPC/E water model.
• Analyzed the liquid-vapor interface structure and the momentum distributions of evaporated molecules.
• Projected trajectories onto key coordinates to simplify the characterization of the TSE.

Main Results:

• Identified the TSE members as having liquid-vapor interfaces with predominantly negative mean curvature at the evaporation site.
• Found that evaporated water molecules possess Maxwellian translational and angular momentum distributions at the liquid's temperature.
• Demonstrated that evaporation trajectories can be effectively described by a simple ballistic escape model from a deep potential well.

Conclusions:

• The evaporation process is primarily governed by the cohesive strength of the liquid, with no significant additional energy barrier.
• The findings support a near-unity condensation probability for water molecules encountering a liquid droplet.
• Results align with prior simulations and some experimental observations, highlighting the predictive power of TPS in studying phase transitions.