Dynamical Studies of Ultrafast Charge Migration in Diatomic and Modular Molecules Probed by Photoelectron Angular Distributions

The recent developments in the generation of optical attopulses suggest that it will soon become experimentally feasible to induce and subsequently directly probe ultrafast charge transfer between the end moieties of the modular molecule. One ultrafast pulse creates a non-stationary state of the neutral or of the cation and a second one ionizes it. Such experiments would allow characterizing a purely electronic time scale, before the coupling to the nuclei takes place. This is a pre Born-Oppenheimer regime where the electronic states are not stationary.[1]

We will report on the simulation of realistic pump probe experiments that monitor the ultrafast electronic dynamics in LiH,[2,3] in the medium size bifunctional molecule PENNA (C₁₀H₁₅N)[4] (Fig.1), C₆₀ and other medium size molecules using a coupled equation scheme that includes the ionization continua and field effects. We show that in a short IR pump- XUV attosecond pulse train (APT) scheme that the APT can be used to disentangle the coherent superposition of states built by the IR pump pulse, acting as frequency filter.[2] The density motion between the two ends of a molecular system is probed by the anisotropy ionization parameter computed as the normalized difference between the ionization yields at the two moieties.[4] Heatmaps of the ionization anisotropy parameter as a function of the delay time between the two pulses and the kinetic energy of the photoelectron exhibit oscillations that reflect the beating periods of the electron density.