Measurement of hydroxyl radicals in an atmospheric pressure discharge plasma by using laser-induced fluorescence

Hydroxyl radicals were measured by laser-induced fluorescence (LIF) using a tunable KrF excimer laser in an atmospheric pressure discharge plasma. In that LIF, all of the OH (A/sup 2//spl Sigma/-X/sup 2//spl Pi/(3,0)) branches were identified within a tunable range of the laser. A time evolution of OH density showed that OH density increased with humidity and oxygen concentration. This results indicates OH radicals were mainly produced by chemical reactions of H/sub 2/O with O radicals. There could be another OH production process other than H/sub 2/O+O/spl rarr/2OH. OH generated by the another reaction reached a peak at about 5 /spl mu/s after discharge. It may have been a collisional dissociation of H/sub 2/O with electrons. OH density augmented after 0.6-/spl mu/s pulsed discharge for several tens /spl mu/s, then decreasing exponentially. The OH lifetime shortened with increasing pressure. This result implies OH were mainly decreased by a reaction with NO/sub 2/ generated from O/sub 2/ and N/sub 2/. Two-dimensional OH distribution was also measured using two-dimensional LIF (2-D LIF) technique. They showed OH radicals proceeded uniformly along a discharge path, then decreasing with horizontal diffusion.