Photodissociation of the Hydroxyl Radical (OH)
The hydroxyl radical (OH) is sort of a piece of a molecule. It has one oxygen atom and one hydrogen atom. One way to make OH is to knock a hydrogen atom off of a water molecule (H2O).
This movie shows how ultraviolet "light" can break apart the hydroxyl radical. You need the latest version of the Flash player to see this movie.
Photons are little bits of light. Photons carry energy.
When a photon hits the hydroxyl radical, it adds energy to the radical. The radical has chemical bonds (they work a bit like stretchy rubber bands!) holding its atoms together. Sometimes the energy from the photon breaks the bond between the oxygen atom and the hydrogen atom. The atoms fly apart!
When a photon knocks molecules (or the hydroxyl radical) apart, it is called photodissociation.
Photons of ultraviolet (UV) light carry more energy than photons of visible light carry. It takes high-energy UV photons to break the hydroxyl radical apart!
Photodissociation of Water
Photodissociation of Oxygen
Photodissociation of Nitrogen
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