Optical Study of Active Species Produced by Microwave Discharge in Water

Microwave plasma was generated on top of the electrode by applying microwave radiation of 2.45 GHz in water. The light-emitting region and radicals formed by microwave discharge were investigated. The experimental results showed that the light-emitting region of microwave plasma in water increased with increasing microwave power, and conversely, decreased with increasing pressure; bubble around the plasma also became small when pressure was enhanced. OH radicals, H atoms, and O atoms were identified using optical emission spectroscopic analysis. The emission intensity of these radicals and atoms increased with increasing microwave power and decreased with increasing internal pressure of reactor vessel. Moreover, the electron excitation temperature of the plasma increased with electric power from 3300 to 4100 K and decreased with pressure from 4300 to 4100 K in comparison with the intensities of H α and H β .