Interplay of the volume and surface plasmons in the electron energy loss spectra of C60_{60}

The results of a joint experimental and theoretical investigation of the C60 collective excitations in the process of inelastic scattering of electrons are presented. The shape of the electron energy loss spectrum is observed to vary when the scattering angle increases. This variation arising due to the electron diffraction of the fullerene shell is described by a new theoretical model which treats the fullerene as a spherical shell of a finite width and accounts for the two modes of the surface plasmon and for the volume plasmon as well. It is shown that at small angles, the inelastic scattering cross section is determined mostly by the symmetric mode of the surface plasmon, while at larger angles, the contributions of the antisymmetric surface plasmon and the volume plasmon become prominent.Comment: 11 pages, 3 figure

Vacancy decay in endohedral atoms: the role of non-central position of the atom

We demonstrate that the Auger decay rate in an endohedral atom is very sensitive to the atom's location in the fullerene cage. Two additional decay channels appear in an endohedral system: (a) the channel due to the change in the electric field at the atom caused by dynamic polarization of the fullerene electron shell by the Coulomb field of the vacancy, (b) the channel within which the released energy is transferred to the fullerene electron via the Coulomb interaction. % The relative magnitudes of the correction terms are dependent not only on the position of the doped atom but also on the transition energy \om. Additional enhancement of the decay rate appears for transitions whose energies are in the vicinity of the fullerene surface plasmons energies of high multipolarity. % It is demonstrated that in many cases the additional channels can dominate over the direct Auger decay resulting in pronounced broadening of the atomic emission lines. % The case study, carried out for Sc$^{2+}$@C$_{80}^{6-}$, shows that narrow autoionizing resonances in an isolated Sc$^{2+}$ within the range \om = 30... 45 eV are dramatically broadened if the ion is located strongly off-the-center. % Using the developed model we carry out quantitative analysis of the photoionization spectrum for the endohedral complex Sc$_3$N@C$_{80}$ and demonstrate that the additional channels are partly responsible for the strong modification of the photoionization spectrum profile detected experimentally by M\"{u}ller et al. (J. Phys.: Conf. Ser. 88, 012038 (2008)).Comment: 32 pages, 11 figure

Formalism of collective electron excitations in fullerenes

We present a detailed formalism for the description of collective electron excitations in fullerenes in the process of the electron inelastic scattering. Considering the system as a spherical shell of a finite width, we show that the differential cross section is defined by three plasmon excitations, namely two coupled modes of the surface plasmon and the volume plasmon. The interplay of the three plasmons appears due to the electron diffraction of the fullerene shell. Plasmon modes of different angular momenta provide dominating contributions to the differential cross section depending on the transferred momentum.Comment: 11 pages, 2 figures; submitted to the special issue "Atomic Cluster Collisions: Structure and Dynamics from the Nuclear to the Biological Scale" of Eur. Phys. J.

Ion-impact-induced C-60 fragmentation

Reinkoster A, Werner U, Lutz HO. Ion-impact-induced C-60 fragmentation. EUROPHYSICS LETTERS. 1998;43(6):653-658.We studied the fragmentation behaviour of C-60 in collisions with fast (100-300 kV q) H+, He+, Ar+, Ar2+ and Ar3+ ions. The multi-particle detector used in this experiment allows to establish coincidences between several correlated fragment ions. Besides the well-known features as multiple ionization and evaporation of C-2n the "fission" into C-60-2n(q+)+C-2n(+) and multi-fragmentation into small charged fragment ions are observed in the coincidence spectra. The fragmentation patterns show a strong dependence on the projectile type

Ion-impact–induced

We studied the fragmentation behaviour of C60 in collisions with fast (100–$300\,{\rm kV}\cdot q$) $\rm H^+$, $\rm He^+$, $\rm Ar^+$, $\rm Ar^{2+}$ and $\rm Ar^{3+}$ ions. The multi-particle detector used in this experiment allows to establish coincidences between several correlated fragment ions. Besides the well-known features as multiple ionization and evaporation of ${\rm C}_{2n}$ the “fission” into ${\rm C}_{60-2n}^{q+}+{\rm C}_{2n}^+$ and multi-fragmentation into small charged fragment ions are observed in the coincidence spectra. The fragmentation patterns show a strong dependence on the projectile type

Auger cascades versus direct double Auger: relaxation processes following photoionization of the Kr 3d and Xe 4d, 3d inner shells

The relaxation processes after non-resonant inner-shell photoionization are studied experimentally using electron–electron time-of-flight coincidence spectroscopy. Results for krypton 3d and xenon 4d as well as 3d photoionization are presented. The experimental data make it possible to disentangle sequential from simultaneous processes using the different electron emission characteristics as the differentiating property. For the population of final states having charges higher than 2, the measurements show a strong preference for sequential Auger cascade decay. Clear evidence for direct double Auger processes is found in the case of Xe 3d photoionization only