Molecular growth of PAH-like systems induced by oxygen species: experimental and theoretical study of the reaction of naphthalene with HO (2Π3/2), O (3P), and O2 (3Σg-)

To assess if reactions with oxygen species can induce a mass increase of polycyclic aromatic hydrocarbons, we exposed naphthalene molecules to an oxidative gas flow containing the radicals H and HO ((2)Pi(3/2)) and the diradicals O (P-3) and O-2 ((3)Sigma(-)(g)). We observed the formation of 1- and 2-naphtol, 1,4-naphthoquinone, naphthalene-derived cyclic ethers, an ester from ring opening, and ether adducts containing two naphthalene units. We investigated the possible reaction pathways as a function of temperature by density functional calculations. We found that the reactivity is characterized by HO, O and H addition to naphthalene, or by H abstraction from it, with roles depending on temperature. In conclusion, oxygen species can promote, under the experimental conditions, mainly naphthalene oxidation and, to a lesser extent, substantial molecular growth, with an efficiency that the calculations indicate to depend on the system temperature. Future experiments should try to quantify key species to allow defining the relative importance of the various reaction mechanisms uncovered by ab initio calculations.