Relationship between photon energy and current induced by photo-excited desolvation of hydrated electrons in atmospheric-pressure dc glow discharge*

Hydrated electrons are generated by plasma-liquid interaction. However, there have been limited reports on the detection of hydrated electrons in liquids interacting with plasmas. The difficulty is caused by the fact that hydrated electrons generated by the plasma irradiation are localized in a narrow region with a thickness of several nanometers below the plasma-liquid interface. To overcome the difficulty, we have developed a method to detect hydrated electrons in the interfacial region. Hydrated electrons in the interfacial region are converted to free electrons when they are irradiated with laser beam having a photon energy exceeding the desolvation energy. Free electrons produced by the desolvation are ejected into the gas phase.

In a previous work, we used an atmospheric-pressure helium dc glow discharge with a liquid electrode, and observed the pulsed increase in the discharge current when the liquid electrode was irradiated with a Nd:YAG laser pulse. In this experiment, we used a dye laser to examine the relationship between the increase in the discharge current and the photon energy. In addition, we estimated the depth profile of hydrated electron density with the help of a numerical simulation on the collisional transport process of free electrons in water.