Combined orbital tomography study of multi-configurational molecular adsorbate systems

Abstract

Molecular reactivity is determined by the energy levels and spatial extent of the frontier orbitals. Orbital tomography based on angle-resolved photoelectron spectroscopy is an elegant method to study the electronic structure of organic adsorbates, however, it is conventionally restricted to systems with one single rotational domain. In this work, we extend orbital tomography to systems with multiple rotational domains. We characterise the hydrogen evolution catalyst Co-pyrphyrin on an Ag(110) substrate and compare it with the empty pyrphyrin ligand. In combination with low-energy electron diffraction and DFT simulations, we fully determine adsorption geometry and both energetics and spatial distributions of the valence electronic states. We find two states close to the Fermi level in Co-pyrphyrin with Co character that are not present in the empty ligand. In addition, we identify several energetically nearly equivalent adsorption geometries that are important for the understanding of the electronic structure. The ability to disentangle and fully elucidate multi-configurational systems renders orbital tomography much more useful to study realistic catalytic systems.

Ferrous to Ferric Transition in Fe‐Phthalocyanine Driven by NO2 Exposure

“…Within the PT approach, the square modulus of the Fourier transform (FT) of the real space molecular orbitals can be directly related to the measured momentum distribution of the photoemitted electrons (momentum map) at defined binding energy (BE) [29, 31–33] . As a result, this procedure allows to unequivocally assign an experimental valence band feature to a specific molecular frontier orbital.…”

Molecular anchoring stabilizes low valence Ni(i)TPP on copper against thermally induced chemical changes

“…43 Thus, this relation provides a one-to-one correspondence between the angular distribution of the photocurrent and the molecular orbitals in the reciprocal space. In this way, molecular orbitals can be identified from their momentum pattern [54][55][56][57] or their wave functions can be retrieved using iterative computational procedures 58,59 (for further details see the Methods section).…”

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

“…Given that the level alignment and thus charge transfer follow from intrinsic properties of the molecule and the substrate, only subtle changes induced by different adsorption configurations are to be expected for large organic adsorbates. 11 − 16 Exceptions are often connected with severe phase changes where elongated planar molecules with their aromatic rings parallel to the surface (face-on) rotate to an upright standing configuration, with the aromatic system perpendicular to the substrate (edge-on). 17 − 21 …”

“…However, when utilizing the connection between ARUPS intensity maps and the Fourier transform of molecular orbitals, known as photoemission tomography (PT), 23 ARUPS has been utilized to simultaneously reveal the electronic and geometric structure for a number of organic adsorbate systems. 16 , 24 − 29 …”