Density and production of NH and NH2 in an Ar–NH3 expanding plasma jet

Abstract

The densities of NH and NH2 radicals in an Ar–NH3 plasma jet created by the expanding thermal plasma source were investigated for various source-operating conditions such as plasma current and NH3 flow. The radicals were measured by cavity ringdown absorption spectroscopy using the (0,0) band of the AΠ3←XΣ−3 transition for NH and the (0,9,0)-(0,0,0) band of the ÃA12←X̃B12 transition for NH2. For NH, a kinetic gas temperature and rotational temperature of 1750±100 and 1920±100K were found, respectively. The measurements revealed typical densities of 2.5×1012cm−3 for the NH radical and 3.5×1012cm−3 for the NH2 radical. From the combination of the data with ion density and NH3 consumption measurements in the plasma as well as from a simple one-dimensional plug down model, the key production reactions for NH and NH2 are discussed.