Photomolecular Effect: Visible Light Interaction with Air-Water Interface

Despite that water is nearly transparent to visible light, we hypothesize that visible light can directly cleave off water molecular clusters at the air-water interface via a process we call photomolecular effect. We had used this hypothesis to explain why some of the past experiments on solar-interfacial evaporation from porous materials can exceed the apparent thermodynamic limit, calculated based on the energy of the incident light and latent and sensible heat required for water evaporation. In this work, we show that this process happens at the air-water interface by measuring the dependence of photomolecular effect on the wavelength, the angle of incidence, and the polarization of the incident light. We further support the photomolecular effect by measuring the temperature response in water and the vapor phases, Raman and infrared spectroscopy, and multiple pump-probe measurements.