Micro-plasmas as efficient generators of singlet delta oxygen

Abstract

This paper discusses the possibility of producing high concentrations of O 2 (a 1 Δ g ) states at pressures up to atmospheric in rare-gas/oxygen/NO mixtures by using micro-plasmas. Micro-plasmas refer to electric discharges created in very small geometries which have been proven able to operate in DC mode at high pressure and high power loading without undergoing any glow to arc transition. The so-called Micro Cathode Sustained Discharge (MCSD), which is a three-electrode configuration using a Micro Hollow Cathode Discharge (MHCD) as a plasma cathode, can be operated as a non-self-sustained discharge with low values of the reduced electric field and of the gas temperature. As a result, these MCSDs can efficiently generate large amounts of singlet delta oxygen. In Ar/O 2 /NO mixtures, at an oxygen partial pressure of 10 mbar, high values of O 2 (a 1 Δ g ) number density (1.5 10 16 cm -3 ) and of the production yield (6.7 %) can be simultaneously obtained. For lower O 2 partial pressure, yields higher than 10 % have been measured. In He/O 2 /NO mixtures, O 2 (a 1 Δ g ) number densities around 10 16 cm -3 were achieved at atmospheric pressure for flow rates in the range 5-30 ln/mn, which could give rise to new applications.