Measurement of argon excimers, Ar2*, in a cold atmospheric plasma jet using cavity ringdown spectroscopy

Abstract

The argon excimer (Ar2*) species is considered to play an important role in the chemistry of cold atmospheric plasma jets, notably in the formation of reactive oxygen and nitrogen species. In the present work, we demonstrate that cavity ringdown spectroscopy can be used to detect and quantitatively measure Ar2* in the effluent of a cold atmospheric plasma jet, the so-called kINPen-Sci. The spectroscopic features of the 5p π3Πg ← a3Σu+Δν = 0 and 7p σ3Σg+ ← a3Σu+ (ν′ - ν″) systems were clearly identified allowing unambiguous assignment to the Ar2* species. A predominant absorption feature at 512 nm was used to determine the integrated density along the axis perpendicular to the gas flow. Assuming a homogeneous density distribution in the kINPen-Sci effluent, Ar2* densities from 1.8 × 1011 molecule · cm−3 at 0 mm to 1.3 × 1010 molecule · cm−3 at 4.2 mm below the nozzle tip were determined.