Even-odd effects in the ionization cross sections of $[{\mathrm{C}}_{60}{]}_2$ and $\left[{\mathrm{C}}_{60}{\mathrm{C}}_{70}\right]$ dimers

We report strong even-odd effects in multiple ionization yields of van der Waals dimers in slow ${\mathrm{Xe}}^{30+}+\left[{\mathrm{C}}_{60}{]}_2\right(\left[{\mathrm{C}}_{60}{\mathrm{C}}_{70}\right])\to \cdots +{[{\mathrm{C}}_{60}{]}_2}^{r+}({\left[{\mathrm{C}}_{60}{\mathrm{C}}_{70}\right]}^{r+})$ electron-transfer collisions as functions of $r\le 7$. This behavior may be due to even-odd variations in the sequences of dimer ionization energies as calculated with an electrostatic model including an electrical fullerene-fullerene contact at the $19a_0$ center-center separation in ${[{\mathrm{C}}_{60}{]}_2}^{+}$. Prompt dissociations predominantly yield intact fullerenes ${[{\mathrm{C}}_{60}{]}_2}^{r+}\to {{\mathrm{C}}_{60}}^{r_1+}+{{\mathrm{C}}_{60}}^{r_2+}$ in the same ($r_1=r_2$, even $r$) or nearby ($r_1=r_2\pm 1$, odd $r>1$) charge states.

Figure 1

(Color online) Left: A schematic of the setup. Right: Time-correlations between the first $\left(t_1\right)$ and the second $\left(t_2\right)$ hits on the detector (cf. text).

Figure 2

(Color online) Measured (squares) and simulated (full curves) $(t_2-t_1)$ distributions for ${[{\mathrm{C}}_{60}{]}_2}^{2+}\to {{\mathrm{C}}_{60}}^{+}+{{\mathrm{C}}_{60}}^{+}$ (left) and ${[{\mathrm{C}}_{60}{]}_2}^{3+}\to {{\mathrm{C}}_{60}}^{2+}+{{\mathrm{C}}_{60}}^{+}$ (right) dissociation processes. The simulated curves are for $E_{\mathrm{KER}}=0.44\mathrm{eV}$ with a detection dead time of $45\pm 12\mathrm{ns}$ (left) and for $E_{\mathrm{KER}}=1.1\mathrm{eV}$ with no dead time (right) and yield minima in ${\chi }^2$ (cf. inset/text).

Figure 3

(Color online) Top: Ionization cross sections for fullerene dimers in arbitrary units. Middle: Ionization energies (IE) for monomers and dimers [modeled as two conducting spheres with $(엯)$ and without (dashed curve) mutual electrostatic interactions]. Below: Deviations from linear $r$ dependencies for dimer ionization cross sections (left scale) and ionization energies (right scale).