The 351.1 nm photoelectron spectrum of the vinyldiazomethyl anion has been measured. The ion is generated through the reaction of the allyl anion with N2O in helium buffer gas in a flowing afterglow source. The spectrum exhibits the vibronic structure of the vinyldiazomethyl radical in its electronic ground state as well as in the first excited state. Electronic structure calculations have been performed for these molecules at the B3LYP/6-311++G(d,p) level of theory. A Franck-Condon simulation of the (2)A'' state portion of the spectrum has been carried out using the geometries and normal modes of the anion and radical obtained from these calculations. The simulation unambiguously shows that the ions predominantly have an E conformation. The electron affinity (EA) of the radical has been determined to be 1.864 +/- 0.007 eV. Vibrational frequencies of 185 +/- 10 and 415 +/- 20 cm(-1) observed in the spectrum have been identified as in-plane CCN bending and CCC bending modes, respectively, for the (2)A'' state. The spectrum for the (2)A' state is broad and structureless, reflecting large geometry differences between the anion and the radical, particularly in the CCN angle, as well as vibronic coupling with the (2)A'' state. The DFT calculations have also been used to better understand the mechanism of the allyl anion reaction with N2O. Collision-induced dissociation of the structural isomer of the vinyldiazomethyl anion, the 1-pyrazolide ion, has been examined, and energetics of the structural isomers is discussed.