Precise measurement of attosecond dynamics of NO molecular shape resonance

Shape resonance is an important and ubiquitous phenomenon in the process of molecular scattering and photoionization. The study of the attosecond photoemission time delay in the vicinity of the shape resonance is of great significance for understanding its intrinsic origin on a nature time scale of electron motion. In this paper, an advanced attosecond coincidence interferometer consisting of a near-infrared femtosecond light source and an extreme ultraviolet attosecond pulse train is used to study the shape resonance process of the 4s electron of nitric oxide molecules via reconstructing attosecond harmonic beating by measuring the interference of two-photon transitions (RABBIT). The energy dependent effective ionization time delay in the vicinity of the resonance energy region is reported. By comparing the relationship between the two-photon transition delay and the one-photon transition delay, it is found that the Wigner delay of the single-photon process is the main reason for the two-photon transition delay changing with energy. The effect of continuum-continuum delay is further explored. Theoretical calculations of the initial state (bound state) and final state (resonance state) electron wave function orbits of the resonance show that the shape resonance assisted time delay is dominated by the electrons trapped in the centrifugal potential barrier.