The Photochemistry reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Photochemistry

Photochemistry is the study of the interaction of light and chemicals.

Vincenzo Balzani's proposes as a first law of photochemistry: "For a photochemical reaction to exist, the chemical in question must absorb light at the frequency used for irradiation."

For example, green grass is green because chlorophyll (an organometallic complex) absorbs other types of light but reflects green. If you try to grow plants under green light (460nm to 600nm) - they will reflect it all and not be able to photosynthesise. No photochemical reaction will have occurred.

Photochemists use techniques such as:

• Quantum yield - finding what proportion of molecules react when a known flux of light is used to irradiate them.
• Flash Photolysis - using a high intensity Xenon flash lamp to initiate a reaction which can then be studied be techniques auch as absorption spectroscopy.

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