Photolysis of Pyridazine in the Gas Phase

Abstract

Pyridazine was photolyzed with long wave ultraviolet radiation (3650–3663 Å) over the temperature range 100–160 °C. Nitrogen and vinylacetylene were the main products, their quantum yields at 110 °C being 0.12 ± 0.05 and 0.09 ± 0.04, respectively. Nitrogen formation is not significantly inhibited by the presence of oxygen and no isomerization of cis-but-2-ene was observed during photolyses. It appears that some reaction occurs from the excited singlet, S (n → π*) A, but this state is efficiently deactivated photophysically. It is suggested that vinylacetylene is formed from a C4H4 diradical by means of a 1,3 H-atom migration, and isotope effects observed for the photolysis of pyridazine-d4 support C—H bond fission.