Exploring ultra-fast charge transfer and vibronic coupling with N 1s RIXSmaps of an aromatic molecule coupled to a semiconductor

We present for the first time two-dimensional resonant inelastic x-ray scattering (RIXS)maps of multilayer and monolayer bi-isonicotinic acid adsorbed on the rutileTiO2(110) single crystal surface. This enables the elastic channel to befollowed over the lowest unoccupied molecular orbitals resonantly excited at the N1s absorption edge. The data also reveal ultra-fast intramolecularvibronic coupling, particularly during excitation into the lowest unoccupied molecularorbital-derived resonance. Both elastic scattering and the vibronic coupling loss featuresare expected to contain the channel in which the originally excited electron is directlyinvolved in the core-hole decay process. This allows RIXS data for a molecule coupled to awide bandgap semiconductor to be considered in the same way as the core-hole clockimplementation of resonant photoemission spectroscopy (RPES). However, contrary to RPESmeasurements, we find no evidence for the depletion of the participator channel under theconditions of ultra-fast charge transfer from the molecule to the substrate densities ofstates, on the time scale of the core-hole lifetime. These results suggest that theradiative core-hole decay processes in RIXS are not significantly modified by chargetransfer on the femtosecond time scale in this system.