2-Methylene-2H-azirine (3a) was generated by photolysis of azidopropadiene (2a) and characterized by low-temperature H-1 NMR spectra and IR data of the matrix-isolated substance. Ab initio calculations at the MP2/6-31+G*//MP2/6-31+G* level are reported for 3a as well as for 3-methyl-2-methylene-2H-azirine (3b) and are in good agreement with the experimental results. This is shown by comparison of computed versus measured IR spectra of the azatriafulvenes 3a and 3b. The contribution of a dipolar canonical structure to the resonance hybrid of 3, which is the first example of a heterocyclic triafulvene, is discussed.