Pulsed electron-beam-sustained discharge in oxygen-containing gas mixtures: electrical characteristics, spectroscopy,and singlet oxygen yield

Abstract

The electrical and spectroscopic characteristics of electron-beam-sustained discharge (EBSD) in oxygen and oxygen-containing gas mixtures are studied experimentally under gas pressures up to 100 Torr in a large excitation volume (∼18 L). It is shown that the EBSD in pure oxygen and its mixtures with inert gases is unstable and is characterised by a small specific energy contribution. The addition of small amounts (∼1%-10%) of carbon monoxide or hydrogen to oxygen or its mixtures with inert gases considerably improves the stability of the discharge, while the specific energy contribution W increases by more then an order of magnitude, achieving ∼6.5 kJ L-1 atm-1 per molecular component of the gas mixture. A part of the energy supplied to the EBSD is spent to excite vibrational levels of molecular additives. This was demonstrated experimentally by the initiation of a CO laser based on the O2 : Ar : CO = 1 : 1 : 0.1 mixture. Experimental results on spectroscopy of the excited electronic states O2(a1Δg) and O2(b1Σg+), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O2(a1Δg) state in the afterglow of the pulsed EBSD by comparing with the radiation intensity of singlet oxygen of a given concentration produced in a chemical generator. Preliminary measurements of the singlet-oxygen yield in the EBSD show that its value ∼3% for W ∼ 1.0 kJ L-1 atm-1 is in agreement with the theoretical estimate. Theoretical calculations performed for W ∼ 6.5 kJ L-1 atm-1 at a fixed temperature show that the singlet-oxygen yield may be ∼20%, which is higher than the value required to achieve the lasing threshold in an oxygen—iodine laser at room temperature.