Photosensitization
Photochemistry · Chemistry
Study notes
H₂ doesn't absorb visible light, but with mercury vapour present it dissociates under UV. Explain. Step 1: H₂ has no absorption in the lamp's range — direct photolysis impossible. Step 2: Hg atoms absorb the UV strongly → Hg* (excited). Step 3: Hg* collides with H₂: Hg* + H₂ → Hg + 2H (energy transfer). Step 4: Hg is regenerated — it acted as a photosensitizer, like a catalyst for light.