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This work suggests an approach to a new target of laser control of charge migration in molecules or molecular ions. The target is motivated by the fact that nuclear motions can not only cause decoherence of charge migration, typically within few femtoseconds, but they may also enable the reappearance of charge migration after much longer times, typically several tens or even hundreds of femtoseconds. This phenomenon is called recoherence of charge migration, opposite to its decoherence. The details depend on the initiation of the original charge migration by an ultrashort strong intense pump laser pulse. It may reappear quasiperiodically, with reference period Tr. We show that a well-designed pump-dump laser pulse can enforce recoherences of charge migration at different target times Tc, for example, at Tc ≈ Tr/2. The approach is demonstrated by quantum dynamics simulations of the laser driven electronic and nuclear motions in the oriented linear cation HCCI+. First, the concept is explained in terms of a didactic one-dimensional (1D) model that accounts for the decisive CI stretch. The 1D results are then confirmed by a three-dimensional model for the complete set of the CH, CC, and CI stretches. [ABSTRACT FROM AUTHOR]

Recently, it was shown that a well-designed laser pulse may prepare an oriented linear molecular ion in a specific superposition state of the electronic ground (g) and first excited (e) states, with different amplitudes and non-zero phases. The reconstruction of the initial state, with time resolution of 100 attoseconds (as), yields the subsequent charge migration that proceeds adiabatically, on the attosecond time scale (AACM). We develop the theory for the time evolutions of the axial density and the flux of the electrons, during AACM. The flux is obtained by simple scaling and time-shifting the results for the ‘reference’ scenario with equal amplitudes and zero phases. Application to the system HCCI+confirms periodic AACM of a rather small number (0.663) of valence electrons, from the acetylenic moiety to the domain of the iodine, and back, with period= 1.85 fs. The underlying axial electronic flux is always unidirectional, with maximum absolute value at the border between the acetylenic moiety and the domain of the iodine, close to the local minimum of the axial density of the valence electrons and to its zero time derivative. The theoretical results imply new challenges for experiment, e.g. one should apply optimal control to steer AACM with maximum electronic flux, and one should investigate its initiation with time resolution below 100 as. [ABSTRACT FROM AUTHOR]