Formation of hydrogen-capped polyynes by laser ablation of C60 particles suspended in solution

Laser ablation of C₆₀ particles suspended in hexane or methanol solution has been studied using a Nd:YAG laser (266, 355, 532, and 1064 nm). Insoluble product analysis by Raman spectroscopy showed that C₆₀ particles transformed to graphite-like ones. On the other hand, soluble product analysis by HPLC coupled with UV absorption spectroscopy and GC/MS demonstrated that linear hydrogen-capped polyynes (C_nH₂: n=8, 10, 12) were formed. The dominant C_nH₂ polyyne was C₈H₂ in all cases. The relative abundance of polyynes decreased with increasing wavelength of the Nd:YAG laser, except for 266-nm irradiation in hexane, where the relative abundance of polyynes at 355 nm was greater than that at 266 nm. It was therefore concluded that photochemical processes are more important than thermal ones for the formation of polyynes. The relative abundance of polyynes in hexane was greater than that in methanol. The dependence of relative abundance of polyynes on the particles concentration, laser irradiation time, and laser power was measured in order to obtain information on formation mechanism of polyynes. These results and reported laser photochemical processes of C₆₀ molecules in the gas phase suggested that C₂ radicals produced from C₆₀ are polymerized and hydrogenated to form C₈H₂ and much smaller amounts of C₁₀H₂ and C₁₂H₂.