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

Single-site Double-Core Hole (ss-DCH or K) and two-site Double-Core Hole (ts-DCH or KK) photoelectron spectra including satellite lines were experimentally recorded for the aromatic CH 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 line and its satellites. KK states' positions and assignments are further identified using a core-equivalent model. We predict that, contrary to what has been observed in the CH series of molecules, the KK energy-level ordering in CH does not reflect the core-hole distances between the two holes.