Strong-field ionization and high-order-harmonic generation during polyatomic molecular dynamics of N2O4

We present state-of-the-art ab initio-type computations of strong-field ionization (SFI) and the single-molecule response contribution to high-order-harmonic generation (HHG) in the polyatomic molecule N2O4. The numerical method uses amixed orbital-and grid-based approach to model the multielectron bound states and single-electron continuum. The effects of ionic-core attraction and Coulomb-mediated interchannel coupling are rigorously included. We show that full-dimensionality time-dependent multielectron computations of SFI and HHG in polyatomic molecules are now feasible. The computational results indicate that (a) SFI yields in N2O4 are dominated by a single ionic state (the A(g) state), and are strongly modulated by the N-N stretch coordinate; and (b) the HHG radiating dipole as a function of the N2O4 N-N stretch is dominated by the same, single state. The molecular-beam coincidence measurements presented here support the computational results. Due to the differences in the estimated vibrational amplitude, however, the computations are not in full agreement with previous HHG data.