Probing the Attosecond Photoionization in the Shape Resonance of NO molecules

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 in the nature time scale of electron motion. In this paper, an advanced attosecond coincidence interferometer constructed by a near-infrared femtosecond light source and an extreme ultraviolet attosecond pulse train is used to study the shape resonance process of the 4σ electron of nitric oxide molecules via reconstruction of attosecond harmonic beating by interference of two-photon transitions (RABBIT) measurement. The energy dependent effective ionization time delay in the vicinity of the resonance energy region was 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 change of the two-photon transition delay with energy, and further explores the effect of continuum-continuum delay. Theoretical calculation of the initial state (bound state) and final state (resonance state) electron wave function orbits of the resonance shows that the shape resonance assisted time delay is dominated by the trapped electron in the centrifugal potential barrier.