The term photochemical pertains to chemical processes or reactions that are initiated or influenced by the absorption of light. Photochemical reactions involve the interaction of light, often in the form of ultraviolet or visible radiation, with molecules, leading to changes in their chemical structure or properties. These reactions are distinct from thermal or non-light-induced chemical reactions.
Key characteristics of photochemical reactions include:
Light absorption: Photochemical reactions require the absorption of photons by molecules. This absorption of light energy leads to the promotion of electrons to higher energy states.
Electronic excitation: The absorbed light energy excites electrons within the molecules to higher energy levels. This excited state is often temporary and can result in changes in the molecular geometry or electronic configuration.
Reaction pathways: Once in the excited state, molecules may undergo various reaction pathways, including bond breaking, bond formation, isomerization, or other transformations. These reactions are specific to the nature of the molecules involved.
Chemical species: Photochemical reactions may generate reactive intermediates or products that are not formed in the absence of light. These products can have unique chemical properties and reactivity.
Wavelength sensitivity: Different photochemical reactions are sensitive to specific ranges of wavelengths. For example, ultraviolet light often plays a significant role in initiating photochemical processes.
Examples of photochemical reactions include the dissociation of ozone in the upper atmosphere due to the absorption of ultraviolet radiation from the Sun, the photosynthesis process in plants where light energy is converted into chemical energy, and various photopolymerization reactions used in the curing of certain types of coatings and adhesives.