Monte Carlo calculation of ion, electron, and photon spectra of xenon atoms in x-ray free-electron laser pulses

When atoms and molecules are irradiated by an x-ray free-electron laser (XFEL), they are highly ionized via a sequence of one-photon ionization and relaxation processes. To describe the ionization dynamics during XFEL pulses, a rate equation model has been employed. Even though this model is straightforward for the case of light atoms, it generates a huge number of coupled rate equations for heavy atoms like xenon, which are not trivial to solve directly. Here, we employ the Monte Carlo method to address this problem and we investigate ionization dynamics of xenon atoms induced by XFEL pulses at a photon energy of 4500 eV. Charge-state distributions, photoelectron and Auger electron spectra, and fluorescence spectra are presented for x-ray fluences of up to 10¹³ photons/μm². With the photon energy of 4500 eV, xenon atoms can be ionized up to $+$44 through multiphoton absorption characterized by sequential one-photon single-electron interactions.