The previously recognized "extremely explosive" carbonyl diazide, OC(N-3)2, was prepared as a pure compound and unambiguously characterized by gas-phase IR, matrix IR, and Raman spectroscopy and X-ray crystallography for the first time. The pure substance shows remarkable kinetic stability at room temperature in the gaseous, liquid, and solid states. A melting point of 16 degrees C and vapor pressure of 5.6 mbar at 0 degrees C were determined. Two planar conformers were found in the gas phase, and a composition of 12% anti-syn versus 88% syn-syn conformer in the gaseous equilibrium mixture at room temperature was estimated by matrix IR spectroscopy. In the crystal structure, only the more stable syn-syn conformer was observed. The preference of the syn-syn configuration was supported by DFT calculations.