fotólisis

Photolysis, or fotólisis, is the chemical decomposition of a substance as a result of exposure to light. It most often involves ultraviolet or visible photons, which transfer energy to a molecule, inducing bond cleavage or electronic rearrangements that produce reactive fragments, radicals, ions, or new molecules.

The process starts when a molecule absorbs a photon with sufficient energy to reach an excited electronic state. Depending on the system, the excited state may dissociate directly, transfer energy to other molecules, or relax to reactive intermediates. The outcome depends on the wavelength of light, the absorption properties (cross sections), the quantum yield, and the surrounding chemical environment. Photolysis can be a primary step in a reaction sequence (direct photolysis) or occur after energy transfer from a photosensitizer (sensitized photolysis).

In the natural world, photolysis plays a central role in atmospheric chemistry and biology. The photolysis of ozone and nitrogen dioxide drives cycles that regulate air composition and climate. In biology, the splitting of water during photosynthesis in plants and algae uses light energy to release oxygen and supply electrons for energy conversion. Photolysis is also relevant in environmental science and technological applications, including water treatment and analytical chemistry, where light-induced decomposition of compounds is exploited or needs to be controlled.

Rate and outcome of photolysis depend on light availability and spectral quality, as well as the chemical properties of the substance. Quantitatively, rates are often described using absorption cross sections, quantum yields, and the spectral irradiance of the light source, integrated across relevant wavelengths.