Direct measurements of absolute concentration and lifetime of singlet oxygen in the gas phase by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) spectroscopy was employed to determine the lifetime and absolute concentration of singlet oxygen, O2(1Δg), in the gas phase. O2(1Δg) molecules were generated by gas-phase photosensitization with octafluoronaphthalene. The absolute concentration of O2(1Δg) at total pressure of 0.3 Torr was estimated to be 3 × 10−6 mol dm−3 at 305 K under our conditions using the ground-state oxygen molecule, O2( 3 ∑ g - ), as a quantitative standard. The observed lifetime of O2(1Δg) is 7 s at 0.6 Torr. This is the first report of the gas-phase lifetime of O2(1Δg) observed by EPR.