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Combined orbital tomography study of multi-configurational molecular adsorbate systems

November 20, 2019

The frontier orbitals largely govern chemical reactivity. Researchers from the Physics and Chemistry Departments of the University of Zurich and the Forschungszentrum Jülich studied the hydrogen evolution catalysts Co-pyrphyrin by orbital tomography. Angle-resolved photoelectron spectroscopy (ARPES) data was acquired at the nanoESCA beamline at Elettra Synchrotron and the data was processed to photoelectron momentum maps. Orbital tomography makes use of the simple relation between the molecular orbital initial state and the photoelectron momentum via Fourier transform, which is possible under certain conditions. Combining ARPES and electron diffraction data with high-level DFT calculations and simulations of the photoemission data enabled the complete determination of the adsorbate geometries and identification and characterization of five molecular valence states.
In general, orbital tomography requires all molecules to be oriented in one single configuration (e. e. domain). This is typically only the case in few selected model systems. We extended orbital tomography to multi-configurational systems (in our case 3 different rotational domains) and demonstrate how the individual contributions can be disentangled. We thus make the method accessible to more complex, chemically more relevant systems.

Figure. Angle-resolved photoelectron spectroscopy (ARPES) data and simulated photoelectron momentum maps (PMMs). ae Co-pyrphyrin (CoPyr). fj Pyrphyrin (Pyr). a, f Raw ARPES data on Ag(110) substrate. b, g PMMs after background subtraction and normalisation. c, h Simulated PMMs for indicated adsorption geometries (AG) based on gas-phase DFT data. d, i Incoherent sum of PMMs: CoPyr (AGs 2, 3, 3′ weighted 1.5:1:1), Pyr (AGs 3, 3′ weighted 1:1). e, j Corresponding molecular orbitals.

Reference: Kliuiev, P., Zamborlini, G., Jugovac, M., Gurdal, Y., Arx, K.v., Waltar, K., Schnidrig, S., Alberto, R., Iannuzzi, M., Feyer, V., Hengsberger, M., Osterwalder, J., and Castiglioni, L. (2019). Combined orbital tomography study of multi-configurational molecular adsorbate systems. Nature Commun 10, 5255. (10.1038/s41467-019-13254-7)

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