L2,3-edges absorption spectra of a 2D complex system: a theoretical modelling

L-2,L-3-edges absorption spectra of FePc (I) and FePc(eta(2)-O-2) (II) on Ag(110) have been modelled using the DFT/ROCIS method. Despite disregarding the presence of the substrate, the agreement between experiment and theory is remarkable. Moreover, theoretical results confirm the fraction of II (70%) present on the surface, thus allowing a thorough assignment of each experimental spectral feature. Ground state (GS) theoretical outcomes pertaining to I and II provide an intimate understanding of the electron transfer pathway ruling the I-based catalytic oxygen reduction reaction. DFT/ROCIS outcomes indicate that the lower excitation energy (EE) side of the L-I/II(3) intensity distributions mainly includes states having the GS number of unpaired electrons (two in I and six in II), whereas states with higher/lower spin multiplicity contribute to the L-I/II(3) higher EE side. The occurrence of states involving metal to ligand charge transfer transitions implying low lying empty pi* ligand-based orbitals on the L-I/II(3) higher EE sides have been confirmed.