  The reactivity of water vapor introduced in the flowing post-discharge of an
RF atmospheric plasma torch is investigated through electrical
characterization, optical emission spectroscopy and mass spectrometry
measurements. Due to the technical features of the plasma torch, the
post-discharge can be considered as divided into two regions: an inner region
(inside the plasma torch device) where the water vapor is injected and an outer
region which directly interacts with the ambient air. The main reactions
induced by the injection of water vapor are identified as well as those
indicative of the influence of the ambient air. Plausible pathways allowing the
production of H, OH, O radicals and H2O2 are discussed as well as reactions
potentially responsible for inhomogeneities and for a low DC current measured
in the flowing post-discharge. Keywords: atmospheric post-discharge, H2O plasma
reactivity, RF plasma torch
