Electron-ion correlation effects in strong field ionization

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Summary form only given. One of the key goals of attosecond spectroscopy is to time resolve the multielectron rearrangement that takes place when an electron is removed from a molecule using a short laser pulse. While XUV pulses address core electrons, infrared pulses address valence electrons, and can be used to excite electron dynamics in the valence shells via a strong field ionization process [1].Clearly, the ionization of atoms and molecules in strong low-frequency fields is inherently a multielectron process. Even if only one electron escapes the core, the process, at its heart, involves interaction between all electrons of the original system. These interactions, in turn, can give rise to excitations of the ion. In fact, there is experimental evidence that strong field ionization can generate ions in excited states, for example see [2-5]. Within the standard adiabatic picture of strong field ionization, usually referred to as optical tunneling, it is typically assumed that only one electron is active, while the other electrons remain frozen in the ion. Under this assumption, the only way to excite the molecular ion during ionization is to remove an electron from a lower lying molecular orbital. However, the higher ionization potential corresponding to such processes implies that these channels are exponentially suppressed in general. In light of this, we suggest a new correlation-driven mechanism for the strong field ionization of multielectron atoms and molecules. We show that correlation-induced coupling between the departing electron and the core electrons can help remove the exponential penalty associated with direct ionization, resulting in complex attosecond dynamics of core rearrangement. We develop an analytical theory based on the R-matrix approach [6] for the multielectron, multichannel case, which explicitly incorporates electron-electron interaction throughout the departing electron's motion under the tunneling barrier. We apply our analysis to N2 and CO2 and demonstrate the importance of correlation-induced excitations for these molecules.