Theory of the Photomolecular Effect

TL;DR

This paper introduces a theoretical model explaining the enhanced visible light absorption at water's surface, which leads to increased evaporation rates and suggests photon-induced molecular cluster cleavage as a key mechanism.

Contribution

It provides the first comprehensive theoretical explanation for the photomolecular effect observed at water surfaces, linking photon absorption to molecular cluster cleavage and evaporation.

Findings

Enhanced evaporation rates exceed thermal limits at visible wavelengths.

Peak evaporation occurs at green light wavelengths.

Photon-induced cluster cleavage explains increased surface absorption.

Abstract

It is well-known that water in both liquid and vapor phases exhibits exceptionally weak absorption of light in the visible range. Recent experiments, however, have demonstrated that at the liquid-air interface, absorption in the visible range is drastically increased. This increased absorption results in a rate of evaporation that exceeds the theoretical thermal limit by between two and five times. Curiously, the evaporation rate peaks at green wavelengths of light, while no corresponding absorptance peak has been observed. Experiments suggest that photons can cleave off clusters of water molecules at the surface, but no clear theoretical model has yet been proposed to explain how this is possible. This paper aims to present such a model and explain this surprising and important phenomenon.