Time-dependent analytical R-matrix approach for strong-field dynamics. II. Many-electron systems

Ionization of atoms and molecules in intense low-frequency fields is a multielectron process which may leave the ion in different excited states. Within the adiabatic perspective on strong-field ionization, usually referred to as optical tunneling, electrons remaining in the molecular ion are assumed to be frozen during the ionization process. In this case, the only way to excite the molecular ion during ionization is to remove an electron from a lower-lying molecular orbital. The higher ionization potential corresponding to such processes implies that such channels are exponentially suppressed during tunneling. Here we show that correlation-induced coupling between the departing electron and the core electrons removes the exponential penalty for ionic excitations, resulting in complex attosecond dynamics of core rearrangement during strong-field ionization. We develop a multichannel theory of strong-field ionization and demonstrate the importance of correlation-induced excitations in the multiphoton and tunneling regimes for N-2 and CO2 molecules.