Prospects of Studying Inner-shell Orbital Relaxation with Attosecond X-ray Pulses

Many-body effects induced by x-ray excitation significantly impact electronic structure and ionization processes. Orbital energy shift or chemical shift, resulting from x-ray photoexcitation, is crucial in understanding x-ray spectroscopy. However, its influence on Rabi oscillation dynamics, especially in the x-ray domain, remains underexplored. Intense x-ray pulses from free-electron lasers offer new avenues to investigate orbital relaxation effects. In this study, we employ our Monte Carlo method to investigate x-ray-induced dynamics in Neon using relaxed and unrelaxed orbital models. Extending our Monte Carlo method to account for stimulated emission, we uncover absorption and scattering hot spots, providing XFEL pulse parameters for experimental exploration of orbital relaxation with intense attosecond pulses. Additionally, we discuss potential experimental strategies and future theoretical methodologies aimed at probing and elucidating the timescale of orbital relaxation.