Radiation Generated by the Ultrafast Migration of a Positive Charge Following the Ionization of a Molecular System

Electronic many-body effects alone can be the driving force for an ultrafast migration of a positive charge created upon ionization of molecular systems. Here we show that this purely electronic phenomenon generates a characteristic IR radiation. The situation when the initial ionic wave packet is produced by a sudden removal of an electron is also studied. It is shown that in this case a much stronger UV emission is generated. This emission appears as an ultrafast response of the remaining electrons to the perturbation caused by the sudden ionization and as such is a universal phenomenon to be expected in every multielectron system.

Figure 1

Hole density along the molecular axis of the molecule MePeNNA as a function of time after a localized ionization of the chromophore. The molecular axis is chosen to pass through the longest spatial extension of the molecule. The Hartree-Fock HOMO and $\mathrm{HOMO}-1$ of the molecule are also shown.

Figure 2

Components of the time-dependent dipole moment (upper panel) and the emission spectrum (lower panel) generated by the charge migration process initiated by a localized ionization of the chromophore site of the molecule MePeNNA.

Figure 3

Ionization spectrum of the molecule MePeNNA computed using the ab initio many-body Green’s function method. The contributions of the 1h configuration $(\mathrm{HOMO}{)}^{-1}$ to the cationic states is given in dark gray (red). The contribution of the $(\mathrm{HOMO}-1{)}^{-1}$ configuration in the first two ionic states is shown in light gray (green). The inset is a zoom of the same plot.

Figure 4

Components of the time-dependent dipole moment (upper panel) and the emission spectrum (lower panel) after sudden removal of an electron from the HF HOMO of the molecule MePeNNA. Comparison with the emission spectrum reported in Fig. 2 is shown in the inset.