Effects Of Electron Correlation On The Intense Field Ionization Of Molecules: Effective Potentials Of Time-Dependent Natural Orbitals

We review our effective potential approach based on the multiconfiguration time-dependent (TD) Hartree-Fock (MCTDHF) method to simulate the multielectron dynamics of molecules. According to the formulation of MCTDHF, we introduce the equations of motion for TD natural orbitals {phi(j) (t)} and TD effective potentials v(j)(eff) (t) that determine the fate of the dynamics of phi(j) (t).nu(eff)(j)(t) is separated into the one-body part nu(1)(t) including the interaction with the laser electric field epsilon(t) and the two-body part nu(2, j)(t) originating from electron-electron interaction. The estimated ionization rate for a CO molecule in an intense near-IR field is higher when epsilon(t) turns to the direction from C to O than when epsilon(t) is reversed, which is in agreement with experimentally observed preferential ionization from the C side. The mechanism of the directional anisotropy in tunnel ionization of CO is attributed to a narrow hump near the C nucleus formed in v(5 sigma)(eff)(t) of the 5 sigma HOMO which results from the field-induced change in v(2, 5 sigma) (t). Analysis of effective potentials reveals that the suppression of 5 sigma ionization when epsilon(t) points from O to C is correlated with the enhancement in high-order harmonic generation from 4 sigma HOMO-2. A hump structure is also found in v(HOMO)(eff)(t) of LiH interacting with an intense near-IR pulse, which identifies the ionization mechanism as "asymmetric charge-resonance enhanced ionization."