HREELS investigations of adsorbed $(C59N)2$

The replacement of one C-atom by an N-atom in $C60$ leads to changes of its geometrical and electronic properties. The resulting heterofullerene radical forms $(C59N)2$ dimers in the bulk. We have used high resolution electron energy loss spectroscopy (HREELS) to investigate the vibrational and electronic excitations of this novel modified fullerene which we deposited as a multilayer film on single crystal graphite C(0001). The frequencies of the vibrational modes are generally close to those of $C60,$ except for two new modes which can be attributed to the dimer: an intra-dimer vibration at around 18 meV and a dipole-active mode at 104 meV. The electronic excitation spectrum is also similar to that of $C60$ regarding the interband transitions, despite a broadening due to the lower symmetry in $(C59N)2.$ However, in contrast to $C60,$ the first excitonic excitations seen at 1.55 and 1.75 eV are now dipole allowed.