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

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(a¹Δ_g) and O₂(b¹Σ_g⁺), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O₂(a¹Δ_g) 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.