ABSTRACT
L2,3-edges absorption spectra of FePc (I) and FePc(η2-O2) (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 I/IIL3 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 I/IIL3 higher EE side. The occurrence of states involving metal to ligand charge transfer transitions implying low lying empty π* ligand-based orbitals on the I/IIL3 higher EE sides have been confirmed.
ABSTRACT
A careful choice of the surface coverage of iron phthalocyanine (FePc) on Ag (110) around the single monolayer allows us to drive with high precision both the long-range supramolecular arrangement and the local adsorption geometry of FePc molecules on the given surface. We show that this opens up the possibility of sharply switching the catalytic activity of FePc in the oxygen reduction reaction and contextual surface oxidation in a reproducible way. A comprehensive and detailed picture built on diverse experimental evidence from scanning tunnelling microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, coupled with density functional theory calculations, sheds new light on the nature of the catalytically active molecule-surface coordination and on the boundary conditions for its occurrence. The results are of relevance for the improvement of the catalytic efficiency of metallo-macrocycles as viable substitutes for platinum in the cathodic compartment of low-temperature fuel cells.
ABSTRACT
Density functional molecular cluster calculations have been used to study the adsorption of CO on the alpha-Al2O3-(0001) surface. Substrate and adsorbate geometry modifications, adsorption enthalpies, and adsorbate vibrations are computed. Despite the rather small size of the employed cluster, relaxation phenomena evaluated for the clean surface agree well with experimental measurements and periodic slab calculations and mainly consist of an inward relaxation of the Lewis acid site (Lsa). Different adsorbate arrangements, perpendicular and parallel to the surface, have been considered. Among them, the most state CO chemisorption geometry (delta Hads approximately -13 kcal/mol) is that corresponding to the adsorbate perpendicular to the surface, atop Lsa and C-down oriented. The C-O stretching frequency (nu C-O) computed for such an arrangement is 2158 cm-1, i.e., blue shifted by 44 cm-1 with respect to the free adsorbate. The lack of experimental evidence pertaining to CO interacting with a well-defined alpha-Al2O3(0001) surface prevents the possibility of a direct check of the computed quantities. Nevertheless, low-temperature IR data for CO on alumina powders (Zecchina, A.; Escalona Platero, E.; Otero Areán, C. J. Catal. 1987, 107, 244) indicate for the chemisorbed species a delta nu = 12 cm-1. The adsorbate-substrate interaction relieves some of the Lsa relaxation, even if the Lsa electronic structure is only slightly affected upon chemisorption.
ABSTRACT
Isotope phlebography is performed using 99mTc as pertecnetate, macroaggregates of albumin (MAA) or microspheres of albumin (MISA). The isotope is injected at a dose of 6-10 mCi into the dorsal foot veins. The area studied begins at the knee and is followed successively by the groin, the iliac area and the region of the IVC. A pulmonary scan is performed when MAA or MISA are used. Our method has proven to be reliable in showing 1) thrombosis of the veins of the groin and iliac area, which appear as a 'non visualisation' of the venous tract, 2) delayed transit time of the isotope, 3) visualisation of the superficial circulation (changes and irrgularities). The association of istope phlebography with pulmonary scan is useful for evaluating the femoral-iliac and the vena caval system and for detecting the presence of pulmonary embolism.
