Singlet oxygen photogeneration from X-O2 van der Waals complexes: double spin-flip vs. charge-transfer mechanism

The channeI of singIet oxygen O-2((1)Delta(g)) photogeneration from van der WaaIs compIexes of oxygen X-O-2 has been investigated to discriminate between two possibIe mechanisms based on charge-transfer (CT) or doubIe spin-flip (DSF) transitions. The results obtained in this work for compIexes with X = ethyIene C2H4, 1,3-butadiene C4H6, deuterated methyl iodide CD(3)l, benzene C6H6 and water H2O and for those investigated previously indicate the DSF mechanism as a source of singIet oxygen. The formation of O-2((1)Delta(g)) is observed orgy when the energy of exciting quantum is sufficient for DSF transition. Universally detected Low vibrational excitation of O-2((1)Delta(g)) arising in the photodissociation of van der WaaIs compIexes X-O-2 indicates the DSF mechanism as its source. For complex of ethyIene C2H4-O-2 ab initio calculations of verticaI energy Delta E-vert for DSF and CT transitions have been carried out. The positive results of singIet oxygen formation from C2H4-O-2 can be explained by the DSF but not by the CT mechanism.