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

Hydroxyl radicals were measured by laser-induced fluorescence using a tunable KrF excimer laser in an atmospheric pressure discharge plasma. The temporal behavior of OH radical, generated by a pulsed arc discharge, was measured in the post-discharge region. It was shown that OH radicals were generated by dissociation of H₂O. The dissociation was mainly affected by oxygen concentration because OH density increased with oxygen concentration. The peak of OH density appeared tens of microseconds after discharge. After the peak, OH decreased exponentially with a decay time constant of tens of microseconds. Since oxygen accelerated the OH decay rate, OH was thought to react with products made by oxygen. Two-dimensional OH density distribution was also observed. OH radicals were generated uniformly along a discharge path, and then decreased in number with diffusion