Measurement and simulation of O2(a1Δg) density under low-pressure mercury lamp irradiation

The density of singlet delta oxygen O2(a1Δg) produced under low-pressure mercury lamp irradiation in an oxygen–nitrogen mixture is measured by infrared optical emission spectroscopy and compared with the results of simulations. A 30-cm-long lamp, whose radiation power is 1.9 W for 185 nm light and 12.2 W for 254 nm light, is irradiated in a cylindrical reactor of 8 cm inner diameter with an O2(1–20%)/N2 flow of 3.75–10 L/min. The measurement shows that the O2(a1Δg) density at the reactor outlet is approximately 1–2 ppm under all experimental conditions, regardless of the O2 concentration and the flow rate. The simulation reproduces the measurement results well and within an error of 50%. On the basis of the simulation model, the O2(a1Δg) density can be simply expressed as [O2(a1Δg)] = 2.7 × 10−3I/(1 + 4.2 × 10−4[O2]/[O3]), where I is the illuminance at 254 nm. When [O3]/[O2] ≫ 4.2 × 10−4, [O2(a1Δg)] can be approximated as 2.7 × 10−3I, which is independent of parameters other than I, as shown by the measurement. The O2(a1Δg) densities calculated using these simple expressions agree with the measured O2(a1Δg) densities within an error of 80%.