Simulations of XE spectra: For XE in contrast to RIXS, states and transition moments we need to correspond to a two level problem, involving decay from a single core-ionized state (|CI ) and multiple valence-ionized states (|V I i ), see FIG. . Still the process is initiated by a core-ionization of the electronic ground state and hence start from the same initial conditions as the RIXS process. In the |CI → |V I i emission process, the decay of electron from occupied molecular orbitals (valence or core) with lower binding energy than the ionized core orbital. This is depicted pictorially in FIG. .