The Electronic Absorption Spectrum of the Propargyl Radical

A new system of diffuse bands in the region 2 900 to 3 450 Å has been found during the flash photolysis of propargyl bromide, propargyl chloride, methyl acetylene, allene, and other compounds. Isotopic studies have been carried out with five isotopically labeled parent compounds. The new bands are assigned to the propargyl radical, CH2—C≡CH. The diffuseness of the bands is attributed to predissociation of the radical in the excited state and gives an upper limit of 86.0 kcal/mole for the dissociation energy of the radical.