Carbon nitride nanostructures have been produced by the arc-discharge technique and analyzed by mass spectrometry. A series of structured peaks in the region of masses from 480 up to 600 suggests the existence of heterofullerenes ${\mathrm{C}}_{n-x}{\mathrm{N}}_x(40\le n\le 50)$. The structure and stability of these small fullerenes were theoretically investigated by quantum chemical calculations. The obtained heats of formation indicate that ${\mathrm{C}}_n$ molecules stabilize upon nitrogen substitution. Two ${\mathrm{C}}_{n-x}{\mathrm{N}}_x$ cages are quite stable, with heats of formation per atom approaching that of ${\mathrm{C}}_{\mathrm{60}}$. These molecules could be the seeds of onionlike structures seen in CN materials [Phys. Rev. Lett. 87, 225503 (2001)].

• Received 3 May 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.015501