Photolytic

Photolytic refers to chemical processes driven by the absorption of light, typically ultraviolet or visible radiation. In photolysis, a molecule absorbs a photon, promoting an electron to an excited state. If the absorbed energy exceeds a bond’s dissociation energy or enables a rearrangement, bonds break or new products form. The efficiency of these processes is described by the quantum yield and depends on factors such as light intensity, wavelength, and the molecule’s absorption spectrum.

In atmospheric and environmental chemistry, photolysis is a key mechanism for generating reactive species. Examples include the photodissociation of chlorine-containing compounds, such as Cl2, which produces chlorine radicals that participate in ozone chemistry; and the photolysis of nitrogen dioxide (NO2) to yield nitric oxide (NO) and atomic oxygen, the latter forming ozone (O3) in certain conditions. Water photolysis, H2O + hv, can produce hydroxyl radicals (OH) and hydrogen atoms, a fundamental source of atmospheric oxidants. Photolytic degradation also affects pollutants and pesticides, where light-driven reactions break down contaminants, sometimes forming intermediate products that may be more or less harmful.

Applications of photolytic processes span environmental remediation, atmospheric modeling, and energy research. Photolysis underpins natural atmospheric aging of trace species and is exploited in technologies such as photocatalysis and solar-driven water splitting. The rate and outcome of photolytic reactions depend on light availability, spectral compatibility, solvent or phase, and the presence of sensitizers or catalysts, making photolysis a context-dependent process.