Small-angle X-ray scattering and mass spectrometry studies of γ-irradiated C₆₀ in cyclohexane

Intense (1.42 krad/min) γ-radiolysis of C₆₀ dissolved in cyclohexane (weak magenta-colored solution) to a total dose of 51 krad resulted in the formation of a new compound (muddy red in color) with a solubility of more than 30 times that of saturated C₆₀ in toluene. Low-power, laser desorption Fourier transform mass spectrometry (LD-FTMS) of the product yielded two ions at m/z = 1539 and 1556, which correspond to [C₆₀(cyclohexane)₁₀-xH]⁺ for x = 23 and 6, respectively. Higher power laser desorption conditions as well as collision-induced dissociation experiments of selected ions show the sequential loss of cyclohexene (C₆H₁₀) units. Small-angle X-ray scattering (SAXS) of the dissolved material supports the mass spectrometry results of cyclohexane additions to the sphere. Taken together, the mass spectrometry and SAXS data indicate that the identity of the γ-radiolysis products of C₆₀ in cyclohexane most likely are cyclohexyl adducts of C₆₀, primarily C₆₀(cyclohexane)₁₀. The SAXS data further indicate that some of the C₆₀(C₆H₁₂)_x entities aggregate into dimers in solution. A model is proposed in which cyclohexyl and hydrogen atom radiolysis products attach to C₆₀ across double bonds. These double bonds are possibly those associated with the two top and bottom 5-fold symmetry positions around two opposing pentagons.