Singlet oxygen O2(a1Δg) formation via UV-excitation of isoprene-oxygen C5H8–O2 encounter complexes in gas phase

Photogeneration of singlet oxygen O2(a1Δg) resulted from photoexcitation at 248 and 266 nm of isoprene-oxygen mixtures at elevated oxygen pressure has been investigated. Pulse energy and oxygen pressure dependence of the singlet oxygen yield indicate one-quantum photoexcitation of the encounter complex isoprene-oxygen C5H8–O2 as a source of O2(a1Δg). Suggested mechanism of O2(a1Δg) photogeneration involves direct excitation of complex with simultaneous change of both partner spins like that observed in van der Waals complex C5H8–O2 [Vidma et al., J. Chem. Phys. 137 (2012) 054305]. Other supposed pathways involve collision-induced photogeneration of Herzberg III state O2(A3Δg) or triplet isoprene as the intermediates.

Alexandra P. Pyryaeva and Veniamin G. Goldort and Sergei A. Kochubei and Alexey V. Baklanov

Chemical Physics Letters 2014, 610-611