Foto del docente

Alberto Modelli

Associate Professor

Department of Chemistry "Giacomo Ciamician"

Academic discipline: CHIM/02 Physical Chemistry

Research

Keywords: ETS electronic structures electron transmission photoelectron spectroscopy dissociative electron attachment biodegradability in soil anion states DEAS

The research activity is devoted to the study of electronic structures, orbital interactions and nature of chemical bonds in gas-phase molecular systems. Various electron spectroscopy techniques are used: photoelectron spectroscopy (PES, excited by X or UV radiations) supplies the ionization energy values from the filled orbitals, electron transmission spectroscopy (ETS) supplies the energies of electron attachment to empty orbitals, that is, the negative of the vertical electron affinity values, dissociative electron attachment spectroscopy (DEAS) measures the abundance of negative fragments produced by electron impact, as a function of the incident electron energy. The experimental data are interpreted with the aid of proper theoretical calculations.



       The research activity is devoted to the study of electronic structures, orbital interactions and nature of chemical bonds in gas-phase molecular systems. Various electron spectroscopy techniques are used: photoelectron spectroscopy (PES, excited by X or UV radiations) supplies the ionization energy values from the filled orbitals, electron transmission spectroscopy (ETS) supplies the energies of electron attachment to empty orbitals, that is, the negative of the vertical electron affinity values, dissociative electron attachment spectroscopy (DEAS) measures the abundance of negative fragments produced by electron impact, as a function of the incident electron energy. The experimental data are interpreted with the aid of proper theoretical calculations.

       A complete picture of the electronic structure requires the knowledge of both the filled and the empty levels, equally important from the thoretical and the reactivity points of view. However, while ionization energy data are easily available in the literature, the complementary electron affinity data are still sparse. The ETS/DEAS apparatus built in Bologna is one of the few existing in the world, and favoured scientific collaborations with researchers of foreign Universities: P.D. Burrow (University of Nebraska, Lincoln,m USA),  K.D. Jordan (University of Pittsburg, USA), H.D. Martin (University of Dusseldorf), M. Tronc (University Pierre et Marie Curie, Paris VI), A.P. Hitchcock (Uni­versity McMaster, Hamilton, Canada), J. Tamariz (University of Mexico City),  L. Szepes e L. Nyulaszi (University of Budapest), J.P. Schermann (University of Paris 13, Villetaneuse), J. Nixon (University of Sussex, Brighton), N.L. Asfandiarov (Academy os Sciences, Ufa, Russia).

We applied the above mentioned techniques to organic and organometallic compounds (a survey is given in A. Modelli, Trends in Chemical Physics (Research Trends) ,  6 (1997) 57-95).

   X-ray photoelectron spectroscopy was used to determine ionization energies from inner pseudo-atomic orbitals, and the subsequent mechanisms of electronic relaxation and charge re-distribution, mainly through shake-up processes, i.e., core ionization accompanied by simultaneous excitation of a valence electron to an empty orbital.

   UV photoelectron spectroscopy was mainly applied to conjugated p-systems and organometallic compounds to investigate on the mechanisms of orbital interactions, nature of chemical bonds, acceptor or donor properties of substituent functional groups, conformational problems.

   Electron Transmission Spectroscopy (an electron-molecule scattering technique) was employed to characterize (in energy and localization properties) temporary anion states, following several lines of research: systematic investigation on the acceptor properties of hydrocarbons containing elements of the main groups (14-17); metal-ligand interactions and charge distributions in transitional complexes; frontier electronic structure in compounds of environmental and biochemical interest.

   When the anion energy is above the threshold for dissociation, the electron capture process (resonance) may follow a dissociative channel (in kinetic competition with simple detachment of the extra-electron). In this case, a long-lived negative fragment and a neutral radical are formed. DEA spectroscopy measures the yield of negative fragments (with a mass filter), as a function of the electron impact energy. In particular, we used DEAS to determine the efficiency of intramolecular electron transfer between non-bonded functional groups. A multidisciplinary approach, including all the above mentioned techniques and theoretical calculations, was employed to characterize the filled and empty level structures of organic monomers and oligomers, extrapolating the results to the corresponding conducting polymers.

       Another field of research is devoted to the determination of the extent and rate of biodegradation of environmental pollutants. In particular, the ASTM D 5988-96 method was used to study the biodegradability of various polymeric materials and ionic liquids due to the action of microorganisms present in the soil, in aerobic conditions.

       The research activity led to publication of more than 165 papers on international journals.