Experimental investigations of radio-frequency discharges in O 2/He/NO mixtures in the pressure range of 1-100 Torr and power range of 0.1-1.2 kW have indicated that O2(a1Δ) production is a strong function of geometry, excitation frequency, pressure and diluent ratio. The goal of these investigations was maximization of both the yield and flow rate (power flux) of O2(a1Δ) in order to produce favorable conditions for application to an electric oxygen-iodine laser (EOIL). At lower pressures, improvements in yield are observed when excitation frequency is increased from 13.56 MHz. As pressure is increased, increasing excitation frequency in the baseline configuration becomes detrimental, and yield performance is improved by reducing the discharge gap and increasing the diluent ratio. Numerous measurements of O2(a1Δ), oxygen atoms, and discharge excited states are made in order to describe the discharge performance dependent on various parameters.