Regenerative Soot-IX: C3 as the dominant, stable carbon cluster in high   pressure sooting discharges
  Results are presented that have been obtained while operating the graphite hollow cathode duoplasmatron ion source in dual mode under constant discharge current. This dual mode operation enabled us to obtain the mass and emission spectra simultaneously. In mass spectra C3 is the main feature but C4 and C5 are also prominent, whereas in emission spectra C2 is also there and its presence shows that it is in an excited state rather than in an ionic state. These facts provide evidence that C3 is produced due to the regeneration of a soot forming sequence and leave it in ionic state. C3 is a stable molecule and the only dominant species among the carbon clusters that survives in a regenerative sooting environment at high-pressure discharges. 
Sohail Ahmad Janjua, M. Ahmad, S. D. Khan, R. Khalid, A. Aleem and   Shoaib Ahmad
physics.plasm-ph