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The formation of singlet oxygen 1O2 provided by the photoexcitation of the encounter complexes of isoprene with oxygen (C5H8-O2) in the gas phase within the spectral region 253.5-355 nm has been observed at the elevated pressure of oxygen. Singlet oxygen has been detected with its NIR luminescence centered near 1.27 μm. The photogeneration of 1O2 is found to be a one-photon process. In the UV-C region (253-278 nm) the quantum yield of 1O2 is measured. This yield of 1O2 is governed mainly by photoexcitation of O2 molecules to the Herzberg III (3Δu) state via enhanced absorption by C5H8-O2 collision complexes. So excited triplet O2 gives rise to singlet oxygen because of triplet-triplet annihilation in the collisions with unexcited O2 molecules. In the UV-B (308 nm) region the appearance of 1O2 is attributed to the excitation of a double spin-flip (DSF) transition in complex C5H8-O2. In the UV-A region (355 nm) besides DSF the O2-assisted T1 ← S0 excitation of isoprene to the triplet state takes place, which is a sensitizer of 1O2 formation. The contribution of the encounter complexes C5H8-O2 to the production of singlet oxygen and to the lifetime of isoprene in the Earth's troposphere are estimated.

In the Comment the authors Y. Nosaka and A. Y. Nosaka present arguments against the mechanism of singlet oxygen production which was suggested in the earlier published paper (Demyanenko et al., J. Phys. Chem. C 2019, 123, 2175) to explain the experimental data for the Near IR (NIR)-luminescence observed to appear after laser excitation at 355 nm of TiO2 suspension in air-saturated solvents CCl4 and H2O. The main arguments of the Comment are directed against Assignment of the NIR Emission and Electron Photodetachment Mechanism suggested by Demyanenko et al.. Particularly the Comment claims that the red shift (near 30 nm) and bandwidth (50-60 nm) of the NIR luminescence observed in paper by Demyanenko et al. are too large to be assigned to the luminescence of singlet oxygen 1O2. In the Reply it is shown that several arguments of the Comment are based on the incorrect statements. The current interpretation of the nature of the red shift and bandwidth of the luminescence of singlet oxygen governed by interact...

Features of the near-infrared phosphorescence of singlet oxygen 1O2 photosensitized by TiO2 in solutions have been investigated. The short-lived phosphorescence of 1O2 with spectral maximum at approximately 1300 nm is observed to follow excitation by pulsed laser radiation at 355 nm of TiO2 suspended in CCl4 and water H2O. The shorter lifetime and spectral shift of this phosphorescence, as compared with phosphorescence of 1O2 sensitized by phenalenone in these solvents, are attributed to the adsorbed state of emitting singlet oxygen. The observed laser pulse energy dependence indicates the two-photon and three-photon nature of this phosphorescence initiation in CCl4 and H2O, respectively. The formation of 1O2 in CCl4 is assumed to be provided by the sequence of one-photon excitation of TiO2, giving rise to superoxide anion O2– and one-photon photodetachment of electron from O2–. The photodetachment of electron from O2– in water H2O is a two-photon process because of higher solvation energy of superoxide a...

The formation of singlet oxygen

The channel of singlet oxygen O2((1)Δg) photogeneration from van der Waals complexes of oxygen X-O2 has been investigated to discriminate between two possible mechanisms based on charge-transfer (CT) or double spin-flip (DSF) transitions. The results obtained in this work for complexes with X = ethylene C2H4, 1,3-butadiene C4H6, deuterated methyl iodide CD3I, benzene C6H6 and water H2O and for those investigated previously indicate the DSF mechanism as a source of singlet oxygen. The formation of O2((1)Δg) is observed only when the energy of exciting quantum is sufficient for DSF transition. Universally detected low vibrational excitation of O2((1)Δg) arising in the photodissociation of van der Waals complexes X-O2 indicates the DSF mechanism as its source. For complex of ethylene C2H4-O2ab initio calculations of vertical energy ΔE(vert) for DSF and CT transitions have been carried out. The positive results of singlet oxygen formation from C2H4-O2 can be explained by the DSF but not by the CT mechanism.

The channel of singlet oxygen O2(1Δg) photogeneration from van der Waals complexes of oxygen X–O2 has been investigated to discriminate between two possible mechanisms based on charge-transfer (CT) or double spin-flip (DSF) transitions. The results obtained in this work for complexes with X = ethylene C2H4, 1,3-butadiene C4H6, deuterated methyl iodide CD3I, benzene C6H6 and water H2O and for those investigated previously indicate the DSF mechanism as a source of singlet oxygen. The formation of O2(1Δg) is observed only when the energy of exciting quantum is sufficient for DSF transition. Universally detected low vibrational excitation of O2(1Δg) arising in the photodissociation of van der Waals complexes X–O2 indicates the DSF mechanism as its source. For complex of ethylene C2H4–O2ab initio calculations of vertical energy ΔEvert for DSF and CT transitions have been carried out. The positive results of singlet oxygen formation from C2H4–O2 can be explained by the DSF but not by the CT mechanism.