Optical spectroscopy diagnostics of discharges at atmospheric pressure

In this paper we review the application of classical optical spectroscopy techniques, optical emission spectroscopy, laser-induced fluorescence (LIF) and absorption, to atmospheric-pressure discharges, with special emphasis on the importance of collision-induced transformations in electronic excited states. Collision processes will be reviewed that are relevant to the main atomic and molecular radicals of interest in the actual application framework. A critical discussion will be devoted to the available rate constant data for collision quenching and vibrational relaxation of N 2 ( C 3 Π u , v = 0–4) and , whose emissions are used for the spectroscopic determination of the reduced electric field by the nitrogen band ratio method. A further detailed discussion will address LIF measurements of OH in unknown He(Ar) + humid air mixtures.