Ion momentum analysis of double ionization of stretched molecules by circularly polarized laser pulses

Using classical ensemble method, we study double ionization (DI) of stretched molecules driven by circularly polarized laser pulses. Classical DI trajectories show that DI is dominated by nonsequential double ionization (NSDI). We find that as R increases, the ion sum-momentum distribution translates from a single-band structure to a three-band structure, and its projection in the direction parallel to the molecular axis changes from a single central peak, to a central-peak with two side shoulders, then to a double-peak. From the ion sum-momentum distributions, the dominant ionization mechanism is identified that translates from collision excitation with subsequent field-ionization (CESI) to collision ionization (CI) as R increases.