  Low-lying relaxation satellites give rise to ultrafast electron dynamics
following outer-valence ionization of a molecular system is studied. To
demonstrate the impact of such satellites, the evolution of the electronic
cloud after sudden removal of an electron from the highest occupied molecular
orbital (HOMO) of the organic unsaturated nitroso compound
2-Nitroso[1,3]oxazolo[5,4-d][1,3]oxazole is traced in real time and space using
ab initio methods only. Our results show that the initially created hole charge
remains stationary but on top of it the system reacts by an ultrafast pi-pi*
excitation followed by a cyclic excitation-deexcitation process which leads to
a redistribution of the charge. The pi-pi* excitation following the removal of
the HOMO electron takes place on a sub-femtosecond time scale and the period of
the excitation-deexcitation alternations is about 1.4 fs. In real space the
processes of excitation and de-excitation represent ultrafast delocalization
and localization of the charge. The results are analyzed by a simple two- and
three-state model.
