Intramolecular Photoelectron Scattering as a Probe of Molecular Geometry

We have studied the influence of core-level photoelectron scattering on neighboring atoms within single gas-phase molecules. We present here a case study of a heteronuclear diatomic molecule, carbon monoxide. Experiment-wise, C 1s photoelectron spectra were recorded in several experiments, performed at SPring-8 (beamline 27SU1) and at SOLEIL synchrotrons (PLEIADES beamline2). The high-resolution spectra were recorded over a broad ionizing photon energy range and the vibrational structure of the single vibrational mode was analysed, in particular the branching ratios within the vibrational envelope of the C 1s photopeak. Beyond the effects of the near-threshold shape resonance, the vibrational branching ratios exhibit a long range oscillatory behavior. As in our other studied cases, these oscillations can be attributed to the modulation of the cross-sections induced by photoelectron scattering on adjacent atoms, in the present case on oxygen. As expected from a scattering phenomenon, the period of the modulation is directly determined by the interatomic distance. We applied different levels of theory to reproduce the observed effects and to test the applicability of the method for investigating the molecula