Photolysis
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Photolysis refers to any chemical reaction in which a compound is broken down by light. The direct process is defined as the interaction of one photon interacting with one target molecule.
Role in Photosynthesis
Photolysis is a part of photosynthesis, which occurs in the granum of the chloroplast. In photolysis the light absorbed by the chlorophyll is turned into chemical energy which is used to split water into hydrogen and oxygen. The oxygen is released as a byproduct while the hydrogen binds with the coenzyme NADP to form NADPH2.
Photolysis in the atmosphere
Photolysis also occurs in the atmosphere as part of a series of reactions by which primary pollutants such as hydrocarbons and nitrogen oxides react to form secondary pollutants such as peroxyacyl nitrates. See photochemical smog.
The two most important photolytic reactions in the troposphere are firstly:
O3 + hν → O2 + O1D λ < 320 nm
which generates an excited oxygen atom which can go on to react with water to give the hydroxyl radical:
O1D + H2O → 2OH
The hydroxyl radical is central to atmospheric chemistry as it initiates the oxidation of hydrocarbons in the atmosphere and so acts like a detergent.
Secondly the reaction:
NO2 + hν → NO + O
is a key reaction in the formation of tropospheric ozone.
In addition, photolysis is the process by which CFCs are broken down in the upper atmosphere to form ozone-destroying chlorine free radicals.
See also
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