Photodissociation of Water (H2O)
This movie shows how ultraviolet "light" can break apart a molecule. 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 a water molecule, it adds energy to the molecule. The molecule 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 one of the hydrogen atoms. The hydrogen atom flies off! All that's left is the piece with one hydrogen and one oxygen (OH). The OH piece is called a hydroxyl radical.
When a photon knocks an atom out of a molecule, 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 water apart!
Photodissociation of Molecular Nitrogen
Photodissociation of Molecular Oxygen
Photodissociation of the Hydroxyl Radical
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