Optical emission spectroscopy characterization of low temperature plasma created in water

Summary form only given. Optical emission spectroscopy has been applied to study characteristics of low-pressure plasma created in water vapour. Plasma was generated by inductively coupled RF generator (RIZ SW-amp.) with the frequency of 13.56 MHz and adjustable output power up to 300 W in a glass discharge tube with the inner diameter of 36 mm. The discharge tube was pumped with a two-stage rotary pump. The water vapour pressure was about 3 Pa. Plasma radiation was measured with a 60 cm optical spectrometer MDR23-Lomo. Emission from highly excited species was found in the ultra-violet, visible and infrared part of the spectra from 200 to 1000 nm. The highest energy of excited radicals was about 15 eV. The rich emission spectra were dominated by atomic transition lines from hydrogen and oxygen: Halpha Hbeta, Hgamma, O(3p5P>3s5S), and O(4p3P>3s3S). Fulcher band molecular hydrogen lines as well as OH (A>X) band were also found. No emission from O₂ and H₂O was detected indicating that the concentration of both molecules in water plasma was low. The observed spectra were explained by collision phenomena in gas phase and on the walls of the discharge tube