Investigation on cluster formation and velocity distribution of evaporating molecules under visible light irradiation*

Understanding and enhancing evaporation is important in developing many industrial applications, such as water desalination technologies and cooling devices. With the aim of precise estimation of evaporation and condensation mass flux at the liquid-vapor interface, many models have been proposed until now. However, most of them assume equilibrium flow at the liquid-vapor interface, although it is known that the evaporated molecules do not follow the Maxwell-Boltzmann distribution, which is the velocity distribution at equilibrium state. To solve this problem, we conducted a molecular beam experiment to obtain the accurate velocity distribution of the evaporated molecules using the time-of-flight method, and successfully confirmed the deviation from the Maxwell-Boltzmann distribution.

Additionally, evaporation under visible light irradiation has been attracting significant attention due to its exceptionally high evaporation rate. It has been hypothesized that in addition to conventional thermal evaporation, the energy of photons cleaves off water molecules in clusters. We aim to clarify the mechanism by detecting the molecular weight of emitted particles with a quadrupole mass spectrometer to examine whether the evaporated water molecules are forming a cluster or not.