Molecular oxygen no relation reactive intermediate
A photoinitiator is a molecule that creates reactive species (free radicals, cations or anions) when exposed to radiation (UV or visible). Synthetic photoinitiators are key components in photopolymers (for example, photo-curable coatings, adhesives and dental restoratives).
Some small molecules in the atmosphere can also act as photoinitiators by decomposing to give free radicals (in photochemical smog). For instance, nitrogen dioxide (NO2) is produced in large quantities by gasoline-burning internal combustion engines. NO2 in the troposphere gives smog its brown coloration and catalyzes production of toxic ground-level ozone (O3). Molecular oxygen (O2) also serves as a photoinitiator in the stratosphere, breaking down into atomic oxygen and combining with O2 in order to form the ozone in the ozone layer.Atmospheric photoinitiators
Peroxides
Since molecular oxygen can abstract H atoms from certain radicals, the HOO· radical is easily created. This particular radical can further abstract H atoms, creating H2O2, or hydrogen peroxide; peroxides can further cleave photolytically into two hydroxyl radicals. More commonly, HOO can react with free oxygen atoms to yield a hydroxyl radical (·OH) and oxygen gas. In both cases, the ·OH radicals formed can serve to oxidize organic compounds in the atmosphere.
H2O2 → 2 ·OH
HOO· + O → O2 + ·OH·OH + CH4 → ·CH3 + H2OMolecular oxygen
In the stratosphere, molecular oxygen (O2) is an important photoinitiator that begins the ozone-production process in the ozone layer. Oxygen can be photolyzed into atomic oxygen by light with wavelength less than 240 nm.
O2 → 2OAtomic oxygen can then combine with more molecular oxygen to form ozone.
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