Vapor phase transmission when water is not electrically heated
In this case, no appreciable difference can be observed because clusters are close to the surface.
Steps to reproduce
We used Cary 5000 UV-VIS-NIR spectrometer to measure the transmission spectrum of the vapor at different heights during light-driven evaporation operation. A special sample stage was made with water-cooled LED so that the sample stage can fit into the sample chamber of the UV-VIS-NIR spectrometer . The probe beam of the spectrometer is limited with an IRIS of the size 1mm (vertical) × 3 mm (horizontal) . The LEDs are fixed in the UV-VIS sample chamber at a 30o angle of incidence and the flux at water surface is 1 sun. During testing, the sample chamber was kept closed to reduce the noise, but vapor can leak out since the sample chamber is not hermetically sealed. Under LED lamp radiation, the detector of the UV-VIS-NIR spectrometer easily gets saturated due to scattered light. To avoid this situation, we put two filters with cut-off wavelengths at 530 nm and 610nm in the front of the detector window to cut off the lights shorter than these wavelengths. We measure the transmission of the air, which we call dry air, after first purging both the sample chamber and the internal chamber of the UV-VIS-NIR spectrometer with nitrogen gas. This spectrum is used as a reference for normalization. Then, we measure the transmittance with the light off, followed by turning the light on, without nitrogen purging in neither the sample chamber or internal of the UV-VIS-NIR. Each spectral scan takes about 15 min.