OH dynamics in a nanosecond pulsed plasma filament in atmospheric pressure He-H₂O upon the addition of O₂

The influence of the addition of O₂ on the OH production in a He + 0.1 % H₂O discharge is investigated using laser induced fluorescence. The plasma properties (T_g, n_e) are reported and used to explain the observed time and spatially resolved OH density, which is absolutely calibrated using Rayleigh scattering. Compared to the case when only H₂O is added, an increase in the measured OH density is observed in the far afterglow. A zero-dimensional chemical kinetic model is constructed, which allows to determine the reactions responsible for the OH production in the far afterglow. When O₂ is admixed, the key reaction O + OH →O₂ + H causes quenching of OH and production of increased densities of H, HO₂ and H₂O₂, which subsequently leads to additional OH production in the late afterglow.