The photomolecular effect, proposed in 2023, claimed that visible light at the air-water interface could directly eject water molecules — a mechanism distinct from thermal evaporation that would enhance evaporation rates under illumination. The claim had specific spectral predictions: absorption features at the air-water interface that differ from bulk water absorption, particularly enhanced absorption at visible wavelengths where bulk water is nearly transparent.
Careful measurements find no such features (arXiv:2603.17977). The interfacial optical absorptance of air-water interfaces matches bulk water absorption within experimental uncertainty across the relevant spectral range. There are no enhanced absorption peaks at visible wavelengths. The spectral signatures that the photomolecular effect predicted — and required — are absent.
This does not prove the photomolecular effect does not exist. It proves that the proposed mechanism — enhanced interfacial absorption at visible wavelengths — does not operate. If visible-light evaporation enhancement is real, it must work through a different mechanism than the one proposed. And if no mechanism can be identified, the original observations of enhanced evaporation must be reexamined for systematic errors.
The measurement is important because the photomolecular effect, if real, would have significant implications for climate science (cloud formation, atmospheric water cycling) and energy technology (solar-driven desalination, passive cooling). Papers building on the claimed effect have been published and cited. Engineering projects have been proposed. The foundation measurement — does the spectral signature exist? — was not performed until now.
The absence of the predicted spectrum is not absence of evidence. It is evidence of absence — specific, quantitative, and falsifying the proposed mechanism. The effect may be real through some other pathway. But the pathway that was published, cited, and built upon is not supported by the spectroscopy.