Intermolecular Coulombic Decay in Endohedral Fullerene at the $4d\to 4f$ Resonance

Intermolecular processes offer unique decay mechanisms for complex systems to internally relax. Here, we report the observation of an intermolecular Coulombic decay channel in an endohedral fullerene, a holmium nitride complex (${\mathrm{Ho}}_3\mathrm{N}$) embedded within a ${\mathrm{C}}_{80}$ fullerene, between neighboring holmium ions, and between the holmium complex and the carbon cage. By measuring the ions and the electrons in coincidence after XUV photoabsorption, we can isolate the different decay channels, which are found to be more prevalent relative to intra-atomic Auger decay.

Figure 1

The schematic of some exemplary ionization and ICD pathways to form ${\mathrm{Ho}}_3\mathrm{N}@{\mathrm{C}}_{80}^{2+}$ are shown above. The binding energies of the orbitals shown are given in the Supplemental Material [23], Table 1. (a) The two-step process of photoionization, with the removal of a photoelectron (PE), and Auger decay (${\mathrm{N}}_{4,5}{\mathrm{O}}_{2,3}{\mathrm{N}}_{6,7}$) of a single ${\mathrm{Ho}}^{3+}$ to form ${\mathrm{Ho}}^{5+}$. The ICD channels between holmium and the ${\mathrm{C}}_{80}$ cage, and between two holmium ions are given in (b) and (c), respectively.

Figure 2

The electron kinetic energy (eKE) distributions at different photon energies, in coincidence with various charge states of the parent molecule [plots (a),(b), and (c)] for photon energies below and above the $4d$ threshold. (d),(e), and (f) The fitted data for electrons detected in coincidence with ${\mathrm{Ho}}_3\mathrm{N}@{\mathrm{C}}_{80}^{+}$ (top), ${\mathrm{Ho}}_3\mathrm{N}@{\mathrm{C}}_{80}^{2+}$ (middle), and ${\mathrm{Ho}}_3\mathrm{N}@{\mathrm{C}}_{80}^{3+}$ (bottom) at a photon energy of 168.8 eV. Lorentz functions, $y=y_0+(2A/\pi )\{w/[4{(x-x_c)}^2+w^2]\}$ are used to fit the peaks, where $w$, $x_c$, and $A$ are the full-width at half maximum (FWHM), the center, and the area, respectively.

Figure 3

The ICD peaks for different charge states for different photon energies normalized by the individual ICD peak maximum.