Time and spatially resolved OH dynamics in a nanosecond pulsed filamentary discharge in atmospheric pressure he-h2o

Summary form only given. Atmospheric pressure plasmas are investigated more and more in view of environmental en biomedical applications. One of the active species that are important for applications such as air cleaning is the OH radical [Kim, H.-H., et al., 2004]. This radical is ubiquitous in the water containing air plasmas and is very efficient due to its high oxidation potential. To investigate the production of OH a nanosecond pulsed filamentary discharge is created in a pin-to-pin electrode configuration in atmospheric pressure He-H₂O mixtures. Different water vapour concentrations are studied and depending on the applied voltage a low- and high-density mode is created [Verreycken, T., et al., 2012]. Time and spatially resolved laser induced fluorescence (LIF) of OH is applied together with time resolved optical emission spectroscopy. With LIF a spatial resolution which exceeds 250 μm is obtained allowing to spatially resolve the OH density in and surrounding the plasma filament. At concentrations higher than 1000 ppm H₂O the chemistry of the He-H₂O discharge is dominated by H₂O. The main properties of the discharge (electron density, gas temperature, electron temperature) are determined to explain the observed OH dynamics. An estimate of the absolute OH density is obtained from a calibration with Rayleigh scattering in N₂ and from a chemical model. In the case of the high-density mode the chemical model indicates that charge exchange and subsequent dissociative recombination can explain the production of OH.