Measurement of Concentration of Singlet Molecular Oxygen in the Gas Phase by Electron Paramagnetic Resonance

The concentration of the lowest excited state of molecular oxygen, O2(1(delta)g), generated by gas-phase photosensitization with octafluoronaphthalene has been determined by electron paramagnetic resonance spectroscopy. The ground-state oxygen molecule, O2(3(sigma)g-), was used as a quantitative standard. At low pressures, (almost equal)0.12 Torr, about 30% of O2(3(sigma)g-) was converted to O2(1(delta)g) under steady-state conditions.