Double-core ionization photoelectron spectroscopy of C6H6: Breakdown of the "intuitive" ortho-meta-para binding energy ordering of K-1K-1 states.

Single-site Double-Core Hole (ss-DCH or K-2) and two-site Double-Core Hole (ts-DCH or K-1K-1) photoelectron spectra including satellite lines were experimentally recorded for the aromatic C6H6 molecule using the synchrotron radiation and multielectron coincidence technique. Density functional theory and post-Hartree-Fock simulations providing binding energies and relative intensities allow us to clearly assign the main K-2 line and its satellites. K-1K-1 states' positions and assignments are further identified using a core-equivalent model. We predict that, contrary to what has been observed in the C2H2n series of molecules, the K-1K-1 energy-level ordering in C6H6 does not reflect the core-hole distances between the two holes.