N_2O ionization and dissociation dynamics in intense femtosecond laser radiation, probed by systematic pulse length variation from 7 to 500 fs

摘要

We have made a series of measurements, as a function of pulse duration, of ionization and fragmentation of the asymmetric molecule N_2O in intense femtosecond laser radiation. The pulse length was varied from 7 fs to 500 fs with intensity ranging from 4 × 10~(15) to 2.5 × 10~(14) W/cm~2. Time and position sensitive detection allows us to observe all fragments in coincidence. By representing the final dissociation geometry with Dalitz plots, we can identify the underlying breakup dynamics. We observe for the first time that there are two stepwise dissociation pathways for N_2O~(3+): (1) N_2O~(3+) → N~+ + NO~(2+) → N~+ + N~+ + O+ and (2) N_2O~(3+) → N_2 ~(2+) + O+ → N~+ + N~+ + O + as well as one for N_2O~(4+) → N ~(2+) + NO~(2+) → N~(2+) + N~+ + O +. The N_2 ~(2+) stepwise channel is suppressed for longer pulse length, a phenomenon which we attribute to the influence which the structure of the ~(3+) potential has on the dissociating wave packet propagation. Finally, by observing the total kinetic energy released for each channel as a function of pulse duration, we show the increasing importance of charge resonance enhanced ionization for channels higher than ~(3+).