On the dynamics of photo-electrons in C₆₀

Abstract

Abstract. We explore photo-electron spectra (PES) and photo-electron angular distributions (PAD) of C 60 with time-dependent density functional theory (TDDFT) in real time. To simulate experiments in gas phase, we consider isotropic ensembles of cluster orientations and perform orientation averaging of the TDDFT calculations. First, we investigate ionization properties of C 60 by one-photon processes in the range of VUV energies. The PES map the energies of the occupied single-particle states, while the weights of the peaks in PES are given by the depletion of the corresponding level. The different influences can be disentangled by looking at PES from slightly different photon frequencies. PAD in the one-photon regime can be characterized by one parameter, the anisotropy. This single parameter unfolds worthwhile information when investigating the frequency and state dependences. We also discuss the case of multi-photon ionization induced by strong infrared laser pulses in C 60 . In agreement with measurements, we find that the PES show a regular comb of peaks separated by the photon energy. Our calculations reveal that this happens because only very few occupied states of C 60 near the ionization threshold contribute to emission and that these few states happen to cooperate filling the same peaks. The PAD show a steady increase of anisotropy with increasing photon order.

VUV photoionization dynamics of the C60 buckminsterfullerene: 2D-matrix photoelectron spectroscopy in an astrophysical context

“…Between 12.0 and 14.0 eV, eight electronic states are expected from theory but in this region, we are unable to obtain a good S/N ratio to decipher anything regarding these states. It is also noteworthy that there are discrepancies between the theoretical works of Colavita et al 30 and Gao et al 67 in this region. Note that comparing the branching ratios between different electronic states intensities between this work and the simulated PES at 14 eV of Gao et al is not straightforward because of the kinetic energy effect on the partial cross sections and the possible presence of autoionization resonances in the TPES.…”

“…split into tunneling states) and with similar intensities so an invocation of D 3d symmetric states might be appropriate but a confirmation would require more work, and is beyond the scope of this paper. There are also some severe discrepancies between its appearance and that of simulated PES, 67 indicating that there is still ground to be made up in the convergence of experiment and theory to the photoelectron spectrum of C 60 .…”

Strong-field effects in the photoemission spectrum of theC60fullerene

“…For the two lowest intensities (I 0 and 2I 0 ), they show a dense sequence of peaks which are separated by the photon energy ω las = 1.36 eV. This is the typical pattern for Above-Threshold Ionization (ATI), which has been well studied for C 60 experimentally [60,61] and theoretically [32,33,62]. These equi-spaced patterns are washed out when the laser in-tensity increases to the two highest values (4.6 I 0 , 8 I 0 ).…”

“…There exist numerous investigations for C 60 [28,29] and other carbon nanostructures such as graphene [30] or nanotubes [31]. An elaborate description of C 60 with an involved orientation averaging is needed for detailed observables such as photo-electron spectra (PES) and photo-angular distributions (PAD) [32][33][34]. A key issue in the present investigations is the ponderomotive motion of the electron in the laser field associated with huge excursions of the electron [35].…”

Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency

“…Additionally, the absence of protons reduces the number of primary ionization pathways. The IE has been calculated and experimentally found to be 7.6 eV [24][25][26][27][28], whereas χ is in the range of 2.6-2.8 eV [29][30][31]. Fullerene-C 60 is thought to be able to store large amounts of energy through rapid conversion of electronic excitation to vibrational excitation because of its many degrees of freedom, thereby enabling delayed ionization processes [32].…”