Strong-field ionization of molecules by few-cycle pulses.

Few-cycle pulses of 800 nm light cause ionization and dissociation of triatomic molecules like H2O and CS2 in the temporal regime where only electron rescattering dominates the laser-molecule interaction. In case of ionization of H2O, significantly higher amounts of kinetic energy are released upon dissociation into atomic fragments. However, the case of CS2 is somewhat special in that the wave packet of the rescattered electron destructively interferes with the antibonding pi orbital of CS2+ such that rescattering is also essentially turned off. Under such circumstances the dissociation channel is absent and long-lived singly, doubly, and triply charged molecular ions dominate the mass spectrum in the few-cycle regime. This brings to the fore the importance of molecular symmetry in strong-field ionization. Ultrafast atomic rearrangements are also observed: H atoms in H2O are rearranged by strong optical fields generated by intense 9.3 fs laser pulses to form a new bond leading to H-2(+); experiments show that this bond formation occurs within a single laser pulse.