Theoretical study of the effects of autoionizing resonances in XUV pump – IR probe photoelectron spectrum of N₂

We provide detailed theoretical investigation of the effects of autoionizing resonances on XUV pump -- IR probe photoelectron spectrum of N₂ by solving the coupled-channel time-dependent Schrodinger equation for coupled electron-nuclear dynamics. N₂ is first excited by ~14.15 eV extreme-ultraviolet (XUV) photons to valence b’¹Σ_u⁺ state. It is then probed by the absorption of two or three near-infrared (NIR) photons (800 nm). The coherent superposition of the wave packet on the valence b’¹Σ_u⁺ state manifests in the beat frequency of the photoelectron spectrum of N₂⁺. Our simulations agree well with the experimental data. In addition, two autoionizing Rydberg states converging to the excited A²Π_u and B²Σ_u N₂⁺ cores are accessed by the resonant absorption of NIR photons via phases and amplitudes of the oscillations of the photoelectron spectrum. This work shows the capability of time-resolved photoelectron spectroscopy as a powerful tool for characterizing the properties of such resonances.