UV-photoexcitation of encounter complexes of oxygen O2–O2 as a source of singlet oxygen O2(1Δg) in gas phase

The photogeneration of singlet oxygen O2(a1Δg) resulted from the photoexcitation at 248 nm of gaseous oxygen at elevated pressure (3–80 atm) has been investigated. Singlet oxygen monitored by its IR-luminescence at 1.27 μm was found to appear via two processes which are identified to be due to absorption of individual O2 molecules and encounter complexes O2–O2, respectively. The one-quantum absorption of complexes gives rise to appearance of oxygen in Herzberg III state O2(3Δu) which is supposed to be a triplet sensitizer responsible for singlet oxygen O2(a1Δg) production observed in our experiments.