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Understanding and control of photon-induced dynamics of molecules on solid surfaces, including atomic rearrangements as well as charge transfer and non-equilibrium electron dynamics, are of essential importance for surface chemistry but also for the development of new devices. We use time-resolved momentum microscopy at a free-electron laser (FEL) and extend orbital tomography to time-resolved imaging of electronic wave functions of excited molecular orbitals. This technique will provide unprecedented insight into the ultrafast interplay between structural and electronic dynamics. In this work we prove general applicability and establish the experimental conditions at FEL sources to minimize space charge effects and radiation damage. We investigate a bilayer pentacene film on Ag(110) by optical laser pump and FEL probe experiments. From the momentum microscopy signal, we obtain time-dependent momentum maps of the molecular valence states that can be related to the molecular initial states by simulations of the involved photoemission matrix elements. A state above the Fermi level is identified which is temporarily occupied after optical excitation.

The amino group of proline is part of a pyrrolidine ring, which makes it unique among the proteinogenic amino acids. To unravel its full electronic structure, proline in solid state and aqueous solution is investigated using X-ray emission spectroscopy and resonant inelastic soft X-ray scattering. By controlling the pH value of the solution, proline is studied in its cationic, zwitterionic, and anionic configurations. The spectra are analyzed within a "building-block principle" by comparing with suitable reference molecules, i.e., acetic acid, cysteine, and pyrrolidine, as well as with spectral calculations based on density functional theory. We find that the electronic structure of the carboxyl group of proline is very similar to that of other amino acids as well as acetic acid. In contrast, the electronic structure of the amino group is significantly different and strongly influenced by the ring structure of proline.

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