UV photolysis of powdered crystals of several aryl azides at cryogenic temperatures afforded azo compounds predominantly. In the cases of p-(N-methylacetamido) phenyl azide and 2- azidobiphenyl, a CH insertion product or a carbazole was formed, competing with azo formation. These products can be considered to be formed through topotactic processes when the crystal structures are taken into account. The arylnitrenes generated in the azide ...