Time-resolved Optical Emission Spectroscopy in Water Electrical Discharges

The characteristics of the plasma initiated in ultrapure water between pairs of tungsten and tantalum electrodes were investigated by time-resolved optical emission spectroscopy. The deexcitation processes of the reactive species formed in the water plasma depended on the electrode material, but had been independent on the polarity of the applied voltage pulses. All the reactive species presented the same evolution with time and have been identified with high concentration in the emission spectra between the pulses. The current-voltage characteristics showed the features of a spark discharge for the both types of electrodes used in the process. When tantalum electrodes were used to generate the discharge, a broad emission continuum (350-940 nm) dominated the spectrum due to a transition to arc discharge.