Microwave plasma generation and filtered transport of O2 (a 1Δg)

Abstract

Singlet oxygen, O2(a 1Δg), is generated using a low pressure, low power continuous microwave discharge operating at 2.45 GHz with a flow of helium seeded with 1–10% molecular oxygen. The absolute concentration of O2(a 1Δg) is measured using off-axis integrated cavity output spectroscopy to probe the Q-branch transition of the (1, 0) band of the Noxon system. In order to remove other energetic species from the flow, the post-discharge flow is passed through a coarse fritted quartz filter. The use of the quartz frit takes advantage of the substantially lower surface sticking probability of O2(a 1Δg) in comparison with other excited species on the flow. Up to 6% of the total oxygen passing through the filter remains in the a 1Δg state, and absolute densities of 2.5 × 1014 cm−3 are obtained using this method. This preparation method and transport is important in developing sources of singlet oxygen for kinetic and spectroscopic studies.