Attosecond phenomena in atomic and molecular systems

We present theoretical quasiclassical studies of attosecond phenomena in 3-electron atoms and diatomic molecules. For 3-electron atoms we predict unusual break-up patterns for small excess energies which have been very recently verified by fully ab-initio quantum mechanical calculations. We discuss how these patterns can be explained in terms of collision sequences and formulate the two-electron attosecond streak camera that allows us to time-resolve a two-electron collision. Furthermore we explore the formation, during Coulomb explosion, of highly excited neutral H atoms for strongly driven H_2 molecules. This process, where after the laser field is turned off an electron occupies a Rydberg state of a hydrogen atom, was reported in a recent experimental study. We find that two-electron effects are important in order to correctly account for the formation of neutral atoms. We show that the formation of a single excited neutral atom H* is possible via two pathways, where either the first or the second ionization step is 'frustrated'. This two single H* formation pathways have distinct traces in the probability distribution of the escaping electron momentum components