Photochemical Reaction
A reaction initiated by the absorption of light, which promotes a molecule to an electronically excited state.
Formula / equation
A + hν → A*
Unit
nm
In depth
Only light of sufficient energy per photon can drive the reaction, so photochemistry is wavelength-selective in a way thermal chemistry is not. Excited states have quite different reactivity from ground states, allowing transformations that would otherwise be thermodynamically impossible.
Examples in the real world
Photosynthesis storing solar energy as glucose; silver halide grains darkening in film; ozone forming in the stratosphere.