 Photochemistry

Photochemistry studies chemical changes initiated or influenced by light. Absorption of a photon can prepare an electronically excited molecule, opening reaction pathways different from those available on its ground-state potential energy surface.^[ref]

The absorbed energy is $E=h\nu$, so changing wavelength changes both which species absorb and which states are reached. Photodissociation of molecular oxygen is an atmospheric example. Absorption alone does not guarantee chemical conversion: relaxation and competing reactions affect the quantum yield. A photon-initiated chain can produce more than one product event per absorbed photon, so a chemical quantum yield need not be at most one.

Photochemistry is a branch of chemistry that studies the chemical effects of light. It focuses on the interactions between light and matter, specifically how light (typically ultraviolet, visible, or infrared radiation) can induce chemical reactions or cause changes in the properties of substances. Key aspects of photochemistry include: 1. **Mechanisms of Light Absorption**: When molecules absorb photons (light particles), they can reach an excited state, leading to various chemical reactions.