Direct Measurement of Internal Energy of Fragmented ${\mathrm{C}}_{60}$

A new experimental approach has been investigated to measure directly the internal energy of fragmented ${\mathrm{C}}_{60}$. Doubly charged $\mathrm{C}_{60}{}^{2+*}$ prepared in collisions ${\mathrm{H}}^{+}+{\mathrm{C}}_{60}\to {\mathrm{H}}^{-}+\mathrm{C}_{60}{}^{2+*}$ decay by evaporation of ${\mathrm{C}}_2$ units. We have measured the internal energy distribution of the transient $\mathrm{C}_{60}{}^{2+*}$ for each decay channel by analyzing the kinetic energy loss of the scattered anion ${\mathrm{H}}^{-}$. This method offers an experimental opportunity for studying the fragmentation dynamics of more complex systems such as larger clusters and biomolecules under internal energy controlled conditions.

Figure 1

(a) 2D spectrum. Horizontal axis: Kinetic energy of ${\mathrm{H}}^{-}$; the point at 2800 eV corresponds to the zero kinetic energy loss. Vertical axis: TOF of recoil ions. (b) Symbols: Projection from (a) onto the horizontal axis of the spots $\mathrm{C}_{60}{}^{2+}$, $\mathrm{C}_{58}{}^{2+}$, $\mathrm{C}_{56}{}^{2+}$, and $\mathrm{C}_{54}{}^{2+}$. Solid lines: Convolution fit of each population distribution with the experimental broadening profile. The population of $\mathrm{C}_{60}{}^{2+}$ in both (a) and (b) is reduced by a factor of 30.

Figure 2

(a) Symbols linked with solid lines $\mathrm{N}(\mathrm{C}_n{}^{2+},E)$: Experimental population distributions of $\mathrm{C}_{58}{}^{2+}$, $\mathrm{C}_{56}{}^{2+}$, and $\mathrm{C}_{54}{}^{2+}$ fullerene fragments as a function of the excitation energy of the transient $\mathrm{C}_{60}{}^{2+}$ ions. Symbols linked with broken lines ${\mathrm{N}}^{\prime }(\mathrm{C}_n{}^{2+},E)$: Theoretical modeling. (b) Probability $\gamma _n{}^{2+}$ for $\mathrm{C}_{60}{}^{2+}$ parent ions with a given internal energy to decay to $\mathrm{C}_n{}^{2+}$ at the time $t=3.5\mu \mathrm{s}$. The lines in this figure are to guide the eyes.