Photodissociation Region · Edge of Starlight
unseel.com · FUV-lit neutral slab · Orion Bar
FUV field G₀ ~ 10⁴
Depth A_V 0
Layer
Ionization front (H II)
FUV photons (6–13.6 eV)
H→H₂ / C⁺→C→CO
[C II] 158 μm cooling
Unseel.com · Photodissociation Regions: Layered Chemistry at the Edge of Starlight