Charge migration in the bifunctional PENNA cation induced and probed by ultrafast ionization: a dynamical study

A full dynamical simulation shows that the charge transfer between the amine and the phenyl moieties of the cation of the bifunctional molecule 2-phenylethyl-N,N-dimethylamine can be induced and subsequently probed by two ultrashort photoionizations. The first ionization of the pump-probe scheme is by a 1.5 fs UV or 6 fs IR pulse that ionizes the neutral. The pump pulse can be tailored to produce a coherent superposition of the electronic states of the cation that differ in their energy and spatial localization of their electron density. The time-dependent amplitudes of the states of the superposition means that the state of the cation is not stationary and we show that it is beating between the two ends of the molecule. This beating is next probed by a second attosecond XUV pulse. The ultrafast photoionization of the cation to the dication probes the spatial charge reorganization in the cation. We use the computed time-dependent molecular frame photoelectron angular distributions as a quantitative measure of the charge migration. The computation of the dynamics are carried out by a coupled equation scheme that includes an electronic manifold for the three charge states: neutral, cation and dication, the coupling to the ionization continua of the cation and the dication and the dynamics induced by the pump and the probe pulses.