Positioning of bound electron wave packets in molecules revealed by high-harmonic spectroscopy.

By solution of the time-dependent two-electron Schrödinger equation, we demonstrate that strong-field ionization in combination with electron correlation can localize bound electron wave packets in molecules. The wave packet creation is revealed by the emission spectrum in high-order harmonic generation, which is sensitive to the ionization and recombination phase difference between different ionization channels. For hydrogen molecules at stretched internuclear distance, we find that the ionization phase difference between the gerade and ungerade channels is in the range from π and 1.5π, indicating that the bound wave packet either is initially on the same side as the outgoing electron or is delocalized.