| Abstract
| - The ozonization mechanism for polycyclic aromatic hydrocarbons (PAHs) and soot is investigated by quantummechanical calculations carried out on molecular and periodic systems. PAHs, interesting per se, serve alsoto model the local features of the graphenic soot platelets, for which another model is provided by a periodicrepresentation of one graphenic layer. A concerted addition leads to a primary ozonide, while a nonconcertedattack produces a trioxyl diradical (in which one of the two unpaired electrons is π-delocalized). Easy lossof (i) 1O2 or (ii) 3O2 from either intermediate, with spin conservation, would yield stable (i) singlet or (ii)triplet π-delocalized species which carry an epoxide group. The trioxyl diradical pathway is estimated to bepreferred, in these systems. An intersystem crossing, taking place in the trioxyl diradicals, can be invoked toallow the even easier loss of a ground-state oxygen molecule with the formation of a ground-state epoxidein a more exoergic and less demanding step. We propose that soot ozonization can take place by such aprocess, with ultimate functionalization of the graphenic platelets by epoxide groups.
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