Franco A. Gianturco#
Laudatio by Charles Joachain#
FRANCO A. GIANTURCO’s international recognition is based on the broad range of topics and research areas into which, over more than forty years, he has made important contributions and laid the theoretical and computational tools for tackling problems that appeared initially to be very different from one another, thereby requiring very different approaches.
One could also say that the "core" of his scientific activities and of his large range of publications can be defined as "MOLECULAR QUANTUM MECHANICS FOR CHEMICAL PROCESSES", which means that he has produced a broad range of theoretical and computational quantum treatments of chemically-oriented physical problems and therefore strived to bridge the existing cultural and "semantic" gaps which tend to exist between quantum physicists and physical chemists when it comes to defininig nanoscopic events and nanoscopic causes at their elementary level.
For the sake of classification, therefore, the main areas of his numerous research contributions could be summarised by the following list of topics:
l. QUANTUM EVALUATION OF MOLECULAR "CHEMICAL " SHIFTS FROM INNER-SHELL SPECTROSCOPY DATA
During the years 1968 to 1976-77 he produced a series of seminal papers, which begun with his work in collaboration with the late Charles Coulson, the Rouse Ball professor of applied mathematics at the University of Oxford, that dealt with the accurate calculations of highly excited molecular ionic states that are obtained in the gas phase by photon-impact inner shell ionization. These states are essentially described as bound states immersed in the many continua of other molecular ions and therefore require a special formulation in order to yield the correct energies : they were important at the time because of the newly produced spectroscopic experiments (ESCA spectra) which linked those energies to small shifts caused by their specific molecular environments ( chemical shifts).The calculations by professor Gianturco allowed for the first time to obtain those small shifts for a series of small polyatornic species and to relate them to the computed charge distributions of the excited ionic states.
2. MULTICHANNEL SCATTERING THEORY OF ELECTRON-MOLECULE COLLISIONS
In the early 70s professor Gianturco started to work on the quantum dynamics of low-energy electrons which are scattered off polyatomic gas-phase targets, thereby leading for the first time to the formulation of the coupled-channel problem in connection with the symmetry group representations of both the scattered electron and the target’s bound electrons. The above analysis led to the possibility of calculating a broad variety of cross sections for many polytomic species of interest in plasma physics, in gas-discharges processes and in the Interstellar medium. The interest in electron scattering processes in polyatomic gases has been a constant interest of the candidate, who has produced in that area, starting in the early 70s, a large number of papers ( more than 250) some of which are listed below.
3. MOLECULAR INELASTIC COLLISIONS FROM CROSSED BEAMS EXPERIMENTS
Starting in the mid 70s the interests of the candidate have also focussed on several aspects of the quantum dynamics that involves rotational and vibrational energy of a partner molecule in collision with a neutral or ionic atom at the relative energies of supersonic crossed beams experiments. In this case, the theoretical formulations involved the production of several possible dynamical approximations which allowed at the time to make direct contact with experiments, thereby linking the results of multichannel scattering calculations with the outcomes of detailed experiments, both in the case of Van der Waals interactions between neutrals and of ionic partners like H+ and D+. In the case of ionic systems the studies of professor Gianturco allowed to produce the first calculations for nonadiabatic dynamics that elucidates the relative flux distributions between inelastic and charge-transfer collion channels in simple systems like H+ with O2 and with N2.
4. NON-EQUILIBRIUM TRANSPORT PROPERTIES IN DILUTED GAS MIXTURES
Another area of interest of the candidate has been the link between the multichannel scattering theory of rotationally inelastic collisions with the non-equilibrium formulation of the Boltzman’s equation, thereby obtaining the broad range of transport cross sections which are involved in computing diffusion, viscosity, thermal conductivity coefficients and, in general, the various momentum-transfer cross sections in gas mixtures containing polyatomic molecules and rare gases like He, Ne and Argon. In this context, the calculations were carried out also in collabotation with collegues in England, in Spain and in Russia, producing a general computational code which calculates such properties and which is now publicly available in the open literature.It is the first code that deals with polyatomic gases as partners to a rare gas bath environment.
5.VERY WEAKLY BOUND VAN DER WAALS TRIMERS
Starting in the early nineties, and in collaboration with a group of physicists in Madrid, the candidate has studied the general problem of accurately producing the few, or only one, bound states that can exist in the gas phase within trimers of either identical or different particles which interact with very weak VdW forces (e.g. the bosonic He trimer). In such special systems the existing bound states could be of a fraction of cm-1 and the ensuing bound wavefunctions could be highly extended in space, thereby providing a big challenge for our capabilities of correctly describing them. In this area the candidate has proposed a variational approach based on an expansion of distributed Gaussian functions (DGF) that has been proved ,through a broad range of examples, to numerically generate both the correct binding energies and the spatial features of the bound wavefunctions. The usefulness of the method has been further related to its potentials in giving indications about the existence of excited Efimov states for such trimers, a subject that has very recently become of great fundamental importance because of its general scaling properties, from the nuclear forces to the Van der Waals interactions.
6. POSITRON-INDUCED MOLECULAR PROCESSES IN GASES
The study of the behaviour of antiparticle beams at very-low energies once they interact with atomic or polyatomic molecular gases has been the subject of greatly renewed experimental interests from the late eighties and early nineties till today. In this area the candidate has developed from the nineties a theoretical and computational framework whereby one can compute rotationally and vibrationally inelastic cross sections involving slow (< l0 eV) electrons and/or positrons and polyatomic molecular gases. Such studies have allowed for the first time to obtain direct comparison, and nanoscopic information, between calculated cross sections and the experimental outcomes so that we now know much more in detail the reasons why the relative efficiencies of the excitation processes vary between leptonic particles and at different collision energies. Furthermore, in the case of positrons the additional channel of particle annihilation produces MeV energy photon emissions that can be related to the structural features of the target molecules. For such processes the candidate has produced for the first time a theoretical model explaining the origin of the observed differences between molecular gases and has carried out calculations which compare the predictions with the experimental findings.
The behaviour of molecular gases in positron scattering reactions is today the physical basis for the modelling of Positron-Emission-Tomography (PET) data.
7. STOCHASTIC STUDIES OF MOLECULAR DOPANTS IN BOSONIC DROPLETS
The appearance of a new set of experimental findings in the nineties that were associated with the use of bosonic He clusters with a large number of atoms ( the droplets) to study the solvation behaviour of single molecules, either neutral or charged, within such cold environments (about 0.3 K) has triggered ,on the part of professor Gianturco, the development of a new computational and theoretical tool to study both the special energetics and the special spatial features of these microsolvation processes. Hence, starting around 1997, the candidate has employed Variational Montecarlo (VMC) and Quantum Diffusion Montecarlo (DMC) methods for the study of linear and nonlinear polyatomic dopants in He droplets. Such studies have led to the discovery of the presence of very different effects induced by cationic and anionic species in the droplets, to the location of alkali-metal dimmers on the surface of the droplets and to the determination ofthe existence of a superfluid fraction of solvent atoms surrounding the dopant molecule.
8. CHEMICAL REACTIONS AT ULTRACOLD TEMPERATURES
Another challenging area of molecular physics which has appeared in the early years of the new Century has been that of the study of molecular interactions and molecular reactions,with neutral and ionic partners, analysed and examined at vanishing energies, i.e. down to possible temperatures of microkelvins and nanokelvins. This new area has presented a new set of challenges also to the theoreticians and professor Gianturco has started around 2001 to study the quantum dynamics of molecular internal cooling by collisions down to the nanokelvins with the most currently used buffer gases, e.g, He, Rb and Cs gases. He has also started to study the features of gas—phase exothermic reactions once the reaction temperature is taken down to the nanokelvins and the scattering reaches the Wigner’s regime. In particular, he has examined the experimental setups produced in magneto-optical traps containing ions, both atomic and molecular ions, in order to predict the most likely outcomes that occur under the presence of a laser cooling frequency for the partner buffer gases. He has also unravelled the special features of neutral reactions down to the nanokelvin regimes, where the effects of virtual state formations is predicted to play a significant role.
9. ROLE OF TRANSIENT ANIONS HW DNA DAMAGE EFFECTS
The appearance in the early 2000’s of a new class of experiments which have linked the occurrence of DNA damage and strand breaks to the formation of metastable anionic species of its molecular components, has also initiated the activity of professor Gianturco in this area so that, starting around 2004, he ha begun to analyse the effects of metastable electron attachments to DNA molecular components in terms of resonance locations, decay times and spatial features. Such analysis has therefore allowed for the first time to link the specific properties of the resonances with the possibility of their decay into fragments containing at least one stable anion, i.e. of Dissociative Electron Attachment (DEA) processes.
l0. QUANTUM ASTROCHEMISTRY STUDIES
The study of that special class of molecular processes which could be linked to what is either observed, or surmised to occur, in the Interstellar Medium or in planetary atmospheres has also been one of the interest of professor Gianturco. Thus, he has initiated a series of quantum calculations on processes linked to the role of Lithium-containing molecules in the Early Universe: the radiative stabilization of LiH, LiH+ and of their electronically excited states, the reactive properties of both LiH and Lil-I+ with H, leading to the formation of H2 molecules, and the study of radiative stabilization of metastable anionic intermediates involving Carbon—rich molecules and deemed to provide the stepping stones for the aggregation reactions that lead to the presence of Polycondensed Aromatic Hydrocarbons (PAHs) in the Interstellar Medium and in planetary atmospheres.
In conclusion, the above, fairly condensed, presentation of the main areas of interest in the research carried out by professor Gianturco and his coworkers, is meant to represent the diversity of topics and variety of theoretical/computational tools employed during his scientific carreer.
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