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

The argon excimer (Ar-2*) 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 Ar-2* in the effluent of a cold atmospheric plasma jet, the so-called kINPen-Sci. The spectroscopic features of the 5p pi(3)Pi(g) <- a(3)Sigma(+)(u)Delta nu = 0 and 7p sigma(3)Sigma(+)(g) <- a(3)Sigma(+)(u) (nu ' - nu '') systems were clearly identified allowing unambiguous assignment to the Ar-2* 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, Ar-2* densities from 1.8 x 10(11) molecule <middle dot> cm(-3) at 0 mm to 1.3 x 10(10) molecule <middle dot> cm(-3) at 4.2 mm below the nozzle tip were determined.