The Stark–Einstein Law is the secondary law of photochemistry.
Statement:
“Each photon of light absorbed by a chemical system causes the excitation of only one molecule.”
Simple Explanation:
- When a molecule absorbs a photon, that photon’s energy excites exactly one molecule.
- This law helps in understanding and calculating how much light is needed to drive a photochemical reaction.
Key Points:
- Photon → Excites → One molecule
- Also called the “Law of Photochemical Equivalence”
- Important for measuring reaction efficiency in photochemistry and designing solar energy devices, photodynamic therapy, and light-driven reactions.
In short: Each absorbed photon excites exactly one molecule, which is essential for understanding light-driven chemical reactions.