The formation of polyhedral carbon ions in fuel-rich acetylene and benzene flames

A great number of different carbon particles with a supposedly closed-shell structure such as C60have have detected in sooting flames. Mass spectra of positive and negative ions of this kind (called polyhedral carbon ions) are presented for low-pressure acetylene- and benzene-oxygen flames. By the use of C6D6it could be confirmed that the particles with an even number of C atoms in fact do not contain hydrogen. Those with an odd number are much less abundant and carry 1 or 2 H atoms. The mass distributions of positive and negative polyhedral ions are quite different, the negative having more and larger particles. Concentration profiles of ions of both signs are reported, and the influence of the C/O ratio and the unburned gas velocity is investigated. The mechanism of formation of these particles is discussed. Arguments are presented that support the working hypothesis that the polyhedral carbon particles are formed from small soot particles rather than by a direct building-up from smaller molecular species.