Influence of water on NO removal by pulsed discharge in N2/H2O/NO mixtures

Kinetic mechanisms of NO removal are studied in N-2/NO and N-2/H2O/NO gas mixtures. A very short duration (60 ns) photo-triggered discharge is used to create a homogeneous plasma at a total pressure between 230 and 460 mbar. Measurements of the NO density are performed in the afterglow by time-resolved laser-induced fluorescence, for a time scale between 2 and 200 mus after the current pulse excitation. Plasma homogeneity allows effective comparison between experimental results and predictions of a fully self-consistent discharge and kinetic modelling. It is shown that the NO removal efficiency is mainly determined through loss mechanisms balance for nitrogen metastable singlet states. In the absence of H2O, NO is in great part dissociated owing to collisions with singlet states. When water vapour is added, these states are destroyed through collisions with H2O with a rate constant k = (3.0 +/- 1.5) x 10(-10) cm(3) s(-1), and it leads to the decrease of the NO removal efficiency. This reaction is invoked for the first time.