Formation of organic triplets from solar irradiation of petroleum

•Triplet energies from solar irradiated petroleum ranged from 280 to 300 kJ/mol.•Triplet abundance in solar irradiated petroleum is greater than that reported for DOM.•Triplet abundance correlated with previously measured singlet oxygen concentrations.

Photochemical production of organic triplets from six different petroleum samples was measured through the cis–trans isomerization of 1,3-pentadiene in Gulf water. The data correlate very well with previously measured singlet oxygen generation rates. Triplet state energies in solar irradiated oil were measured in the range of 280–300 kJ/mol. The photoisomerization state for the petroleum system was reached between 5 and 6 h of irradiation, which is 12 times faster than reported studies for dissolved organic matter. The molar absorptivity for each oil sample showed a weak, negative correlation with the pseudo first order rate constant, k′i, for the cis–trans isomerization. There is a weak, negative correlation between k′i and absorptivity at 300 nm, 350 nm and 400 nm wavelengths (R2 = 0.57, 0.52, 0.54 respectively), which indicates that not all of the chromophores are active in producing triplets. Furthermore those chromophores that do not produce triplets are screening light from the compounds that do.

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