EVALITA Evaluation of NLP and Speech Tools for Italian - December 17th, 2020

Welcome to EVALITA 2020! EVALITA is the evaluation campaign of Natural Language Processing and Speech Tools for Italian. EVALITA is an initiative of the Italian Association for Computational Linguistics (AILC, http://www.ai-lc.it) and it is endorsed by the Italian Association for Artificial Intelligence (AIxIA, http://www.aixia.it) and the Italian Association for Speech Sciences (AISV, http://www.aisv.it)

Bimolecular kinetics according to a stochastic analysis of reactant dynamics

A stochastic representation of the reversible bimolecular process A + B reversible arrow AB is introduced on the basis of the nearest-neighbor distribution. It leads to a description of the reactant pair dynamics under the action of its interaction potential, without introducing any boundary condition or sink function. In this way it becomes evident that reaction processes are particular manifestations of the molecular dynamics. The analysis of the eigenvalues of the time evolution operator allows one to identify the conditions for a well-defined time scale separation between the slow kinetic processes and the fast equilibration of the unbound pair. Correspondingly the rate equations for the reversible bimolecular kinetics are recovered from the long time behavior of the nearest-neighbor distribution. By means of asymptotic methods, analytical approximations are derived for the rate coefficients and their concentration dependence. This allows a simple rationalization of the effects of the interaction potential between the reagents. (C) 2001 American Institute of Physics

Carbon dioxide reduction by heterogeneous and homogeneous electrocatalysts

Direct reduction of CO2, which is a thermodynamically stable and kinetically rather inert molecule, at metallic electrodes requires highly negative overpotentials and results in a variety of products, whose distribution depends on the nature of the electrode material, solvent and background electrolyte as well as on experimental parameters such as CO2 concentration, temeprature and current density. Homogeneous catalysis both by electrogenerated aromatic radical anions and transition metal complexes drastically affects product selectivity. This communication presents examples of CO2 activation both by direct electrode reduction and by homogeneous electrocatlysis, with particular emphasis on the reduction mechanisms

Compared selectivities of redox-catalyzed and direct electrochemical processes Part 2. Reactions in which product selection involves competition between dimerization and deactivation followed by further reduction (or oxidation)

Possible changes in selectivity between redox-catalyzed processes and direct electrochemical reactions are discussed for a typical reaction scheme where product selection involves competition between a dimerization step and a reduction (or oxidation) pathway in which the reductant (or oxidant) is the catalyst on the one hand and the intermediate resulting from the first electron transfer on the other. This second reduction (or oxidation) pathway may or may not be controlled by the transformation of the first electron transfer intermediate into a second intermediate that undergoes a second electron transfer. In the former case, changes in selectivity between the two types of electrolysis conditions arise solely from the space dependence of the reactant and intermediate concentrations. They usaually favor the reduction (or oxidation) pathway in a redox-catalysed process rather than the direct reaction. In the converse situation, where the transformation of the first electron transfer intermediate is reversible and acts as a pre-equilibrium to the second electron transfer, one source of possible changes in selectivity also results from space depenence of the reactant and intermediate concentrations. However, it tends to play an opposite role, favoring the reduction (or oxidation) pathway in the direct reaction rather than the redox-catalyzed process. This effect is amplified if, as is usually the case, the catalyst is a weaker reductant (or oxidant) than the first electron transfer intermediate of the direct electrochemical reaction

Compared selectivities of redox-catalyzed and direct electrochemical processes Part 1. Reactions in which product selection involves competition between dimerization and first-order reactions

In reactions where product selection involves competition between dimerization and first-order steps, selectivity may change on going from direct electrolysis to redox-catalyzed electrolysis. The variation of product distribution with pertinent competition parameters is rigorously and quantitatively established in each case. The physical reasons underlying this prediction are discussed. They are shown to derive from the development of spece-dependent concentration profile of the product selection intermediate. The particular form that this profile takes in each case is a function of the nature and rate of the step that produces the key intermediate and of the rates of the follow-up steps

Homogeneous electron transfer catalysis of the electrochemical reduction of carbon dioxide. Do aromatic anion radicals react in an outer-sphere manner?

Electrochemically generated anion radicals of aromatic nitriles and esters possess the remarkable property to reduce carbon dioxide to oxalate with negligible formation of carboxylated products. They may thus serve as selective homogeneous catalysts for the reduction of CO2 in an aprotic medium. The catalytic enhancement of the cyclic voltammetric peaks of these catalysts is used to determine the rate constant of the electron transfer from these aromatic anion radicals to CO2 as a function of the catalyst standard potential. Substituted benzoic esters allowed a particularly detailed investigation of the resulting activation-driving force relationship. Using 14 different catalysts in this series made it possible to finely scan a range of reaction standard free energies of 0.4 eV. Detailed analysis of the resulting data leads to the conclusion that the reaction is not a simple outer-sphere electron transfer. It rather consists in a nucleophilic addition of the anion radical on CO2, forming an oxygen (or nitrogen for the nitriles)- carbon bond, which successively breaks homolytically, generating the parent ester (or nitrile) and the anion radical of CO2, which eventually dimerizes to oxalate

Mechanism of the electrochemical reduction of carbon dioxide at inert electrodes in media of low proton availability

Direct electrolysis of CO2 in DMF at an inert electrode, such as mercury, produces mixtures of CO and oxalate, whereas electrolysis catalysed by radical anions of aromatic esters and nitriles produces exclusively oxalate in the same medium. Examination of previous results concerning the direct electrochemical reduction and the reduction by photoinjected electrons reveals that there are no significant specific interactions between reactant, intermediates and products on the one hand, and the electrode material on the other, when this is Hg or Pb. These observations and a systematic study of the variations of the oxalate and CO yields with temperature and CO2 concentration, allow the derivation of a consistent mechanistic model of the direct electrochemical reduction. It involves the formation of oxalate from the coupling of two CO2 radical anions in solution. CO (and an equimolar amount of carbonate) is produced by reduction at the electrode of a CO2-CO2= adduct, the formation of which, at the electrode surface, is rendered exothermic by non-specific electrostatic interactions