MCSCF calculations reveal that diazirinyl anion (1), its conventional C-s structure resulting from deprotonation of diazirine (c-CH2N2), is less stable than its open C-2v isomer (2) in which the two nitrogens are no longer bound. The latter species represents a novel type of reactive intermediate, a biradical inion. It is calculated to have a large electron binding energy (0.80 eV) and is an experimentally attractive target. G2 theory has been used to provide the heats of formation of diazomethane and diazirine, two important compounds whose experimental energies are not well established.