(Abstract) “Although water is almost transparent to visible light, we demonstrate that the air–water interface interacts strongly with visible light via what we hypothesize as the photomolecular effect. In this effect, transverse-magnetic polarized photons cleave off water clusters from the air–water interface. We use 14 different experiments to demonstrate the existence of this effect and its dependence on the wavelength, incident angle, and polarization of visible light. We further demonstrate that visible light heats up thin fogs, suggesting that this process can impact weather, climate, and the earth’s water cycle and that it provides a mechanism to resolve the long-standing puzzle of larger measured clouds absorption to solar radiation than theory could predict based on bulk water optical constants. Our study suggests that the photomolecular effect should happen widely in nature, from clouds to fogs, ocean to soil surfaces, and plant transpiration and can also lead to applications in energy and clean water.”
(First paragraph prepub) “The evaporation of water is ubiquitous in nature and industrial technologies. The known mechanism for evaporation is “thermal evaporation” which highlights the energy input for evaporation is via heat. Due to the weak absorption of water to visible light 1,2, the first step to using solar energy to evaporate water is usually by converting it into thermal energy through photothermal processes via additional absorbing materials 3–8. Contrary to this conventional wisdom, we report here strong absorption of photons in the visible spectrum at the water-vapor interface by direct cleavage of water clusters via a process we call photomolecular effect. We show that this process happens at the water-vapor interface by measuring the dependence of the photomolecular evaporation rate on the wavelength, the angle of incidence, and the polarization of the incident light.)
Guangxin et al., Photomolecular effect: Visible light interaction with air–water interface, PNAS, April 23, 2024.
(Paywall) https://www.pnas.org/doi/10.1073/pnas.2320844121
(Prepub) https://arxiv.org/pdf/2310.19832
(Press Release) Chandler, How light can vaporize water without the need for heat, MIT Press, April 23, 2024.
https://news.mit.edu/2024/how-light-can-vaporize-water-without-heat-0423
