Directly observing atomic motions in molecules during chemical dynamics has long
constituted one of the grand challenges in chemistry. 1 The emergence of X-ray free …

We investigate the use of orbital-optimized references in conjunction with single-reference
coupled-cluster theory with single and double substitutions (CCSD) for the study of core …

Understanding the interaction of intense, femtosecond X-ray pulses with heavy atoms is
crucial for gaining insights into the structure and dynamics of matter. One key aspect of …

The Small Quantum Systems instrument is one of the six operating instruments of the
European XFEL, dedicated to the atomic, molecular and cluster physics communities. The …

Inner-shell photoelectron spectroscopy provides an element-specific probe of molecular
structure, as core-electron binding energies are sensitive to the chemical environment. Short …

Excited double-core-hole states of isolated water molecules resulting from the sequential
absorption of two x-ray photons have been investigated. These states are formed through an …

The ultrashort and intense pulses of X-rays produced at X-ray free electron lasers (XFELs)
have enabled unique experiments on the atomic level structure and dynamics of matter, with …

European XFEL is an international facility providing hard and soft x-ray free-electron laser
radiation for user experiments with a wide range of scientific applications. Its …

A theoretical model for investigating the radiative transfer of an x-ray free electron laser
(XFEL) pulse is developed based on a one-dimensional radiative transfer equation. The …

Here, we report on the nonlinear ionization of argon atoms in the short wavelength regime
using ultraintense x rays from the European XFEL. After sequential multiphoton ionization …