Visualization of short-lived reactive species in liquid in contact with atmospheric-pressure plasma by chemiluminescence of luminol

Blue chemiluminescence was observed just below the plasma-liquid interface when an atmospheric-pressure plasma was in contact with an alkaline solution in which luminol was dissolved. The shape of the chemiluminescent area was that of a thin disk. The diameter of the disk was approximately the same as that of the plasma column, and the thickness was roughly estimated to be less than 0.1 mm. The chemiluminescence is considered to originate from the oxidation reaction of luminol by O-2(-) and/or OH. The experimental results reveal that the chemiluminescence of luminol is useful for real-time visualization of plasma-induced short-lived species in liquids. (c) 2018 The Japan Society of Applied Physics