S: http://www4.ncsu.edu/~franzen/public_html/Poland/Poznan08a/Text/Ch6.pdf (last access: 11 December 2013); http://www.thebigger.com/chemistry/chemical-kinetics/define-photochemical-reactions-with-example/ (last access: 1 October 2015).
N: 1. A chemical reaction initiated by the absorption of energy in the form of light. The consequence of molecules’ absorbing light is the creation of transient excited states whose chemical and physical properties differ greatly from the original molecules. These new chemical species can fall apart, change to new structures, combine with each other or other molecules, or transfer electrons, hydrogen atoms, protons, or their electronic excitation energy to other molecules. Excited states are stronger acids and stronger reductants than the original ground states. It is this last property that is crucial in the most important of all photochemical processes, photosynthesis, upon which almost all life on Earth depends. Through photosynthesis, plants convert the energy of sunlight into stored chemical energy by forming carbohydrates from atmospheric carbon dioxide and water and releasing molecular oxygen as a byproduct. Both carbohydrates and oxygen are needed to sustain animal life. Many other processes in nature are photochemical.
2. Although carbon monoxide has also been shown to take part with NOx in similar photochemical reactions, its presence does not lead to significant oxidant formation when hydrocarbons are present.
S: 1. EncBrit – http://global.britannica.com/science/photochemical-reaction (last access: 1 October 2015). 2. TERMIUM PLUS (last access: 1 October 2015).