On the dynamics of photo-electrons in C₆₀

Abstract

We explore photo-electron spectra (PES) and photo-electron angular\ndistributions (PAD) of C$_{60}$ with time-dependent density functional theory\n(TDDFT) in real time. To simulate experiments in gas phase, we consider\nisotropic ensembles of cluster orientations and perform orientation averaging\nof the TDDFT calculations. First, we investigate ionization properties of\nC$_{60}$ by one-photon processes in the range of VUV energies. The PES map the\nenergies of the occupied single-particle states, while the weights of the peaks\nin PES are given by the depletion of the corresponding level. The different\ninfluences can be disentangled by looking at PES from slightly different photon\nfrequencies. PAD in the one-photon regime can be characterized by one\nparameter, the anisotropy. This single parameter unfolds worthwhile information\nwhen investigating the frequency and state dependences. We also discuss the\ncase of multi-photon ionization induced by strong infrared laser pulses in\nC$_{60}$. In agreement with measurements, we find that the PES show a regular\ncomb of peaks separated by the photon energy. Our calculations reveal that this\nhappens because only very few occupied states of C$_{60}$ near the ionization\nthreshold contribute to emission and that these few states happen to cooperate\nfilling the same peaks. The PAD show a steady increase of anisotropy with\nincreasing photon order.\n