Detection of solvated electrons below the interface between atmospheric-pressure plasma and water by laser-induced desolvation

Abstract

We have developed a new method to detect solvated (hydrated) electrons at the plasma–water interface. The method is based on laser-induced desolvation followed by the release of free electrons into the plasma. We employed an atmospheric-pressure dc glow discharge, in which the water surface worked as the cathode, in the experiment. When the region just below the water cathode was irradiated with a pulsed laser beam, we observed the pulsed increase in the discharge current. The increase in the discharge current was caused by the release of free electrons, which were produced from hydrated electrons by the laser-induced desolvation. The pulsed increase in the discharge current was sensitive to the laser wavelength. We compared the relationship between the pulsed increase and the laser wavelength with the distribution of the solvation energy of hydrated electrons using Monte Carlo simulation on the transport of free electrons in water. As a result, it was concluded that hydrated electrons produced under the experimental conditions were located at a distance of 7–15 nm from the plasma–water interface.