Luigi Cerruti

Singlet-singlet electron transitions in isoelectronic monosubstituted benzenes. a semi-empirical study by a modified CNDO—CI method

Abstract A modified CNDO-CI method is presented which assigns the singly excited singlet configurations to the different irreducible representations and separately diagonalizes the resulting blocks in the Hamiltonian CI matrix, using the same number of effectively interacting terms for each irreducible representation (annihilation of interaction terms by the ZDO approximation being duly taken into account). Parameterization has been adjusted to fit a set of 25 experimentally well established O-O transition energies of different monocyclic compounds and the method has been applied to the first four transitions of the isoelectronic set of toluene, aniline, phenol and fluorobenzene. Attention has been paid to changes in dipole moments and in electron charge distributions, using population analysis and electron density maps, after suitable deorthogonalization of the bond order matrix.

Clausius’ Disgregation: A Conceptual Relic that Sheds Light on the Second Law

The present work analyzes the cognitive process that led Clausius towards the translation of the Second Law of Thermodynamics into mathematical expressions. We show that Clausius’ original formal expression of the Second Law was achieved by making extensive use of the concept of disgregation, a quantity which has subsequently disappeared from the thermodynamic language. Our analysis demonstrates that disgregation stands as a crucial logical step of such process and sheds light on the comprehension of such fundamental relation. The introduction of entropy—which occurred three years after the first formalization of the Second Law—was aimed at making the Second Law exploitable in practical contexts. The reasons for the disappearance of disgregation, as well as of other “pre-modern” quantities, from the thermodynamics language are discussed.

Dante’s Bones

This essay will outline a profile of Italian science, against the background of European science, in the period between the Peace of Aachen of 1748 and the annexation of Rome to a unified Italy in 1870. The significance of the choice of two political events to demarcate the study will become clear in the course of the essay, but the dates have a precise historical meaning. After the Peace of Aachen the Peninsula remained fragmented into many States, which nevertheless had stable borders, and for half a century it enjoyed an unusual peace. In 1870 the lay bourgeoisie — and the aristocracy — conquered that Italian city that had for two millennia been a ‘universal’ symbol of power. The two events mark the beginning and end of a notably long period, a historiographical choice that permits the individuation of longstanding relations within and outside the Italian scientific community. At the same time, the geographic heterogeneity of the Peninsula means that in order to follow the vicissitudes of Italian science we shall have to adopt a somewhat ad hoc — although quite specific — interpretation of the center/periphery opposition. It is not at all easy to give a strict definition of what constituted ‘Italy’ in the period considered. Further difficulties are added if we ask who, at that time, could be defined as an ‘Italian scientist’. The two questions will be treated separately.

From Steam Engines to Chemical Reactions: Gibbs' Contribution to the Extension of the Second Law

The present work analyzes the foundations of Gibbs’ thermodynamic equilibrium theory, with the general aim of understanding how the Second Law—as formulated by Clausius in 1865—has been embodied into Gibbs’ formal system and extended to processes involving chemical reactions. We show that Gibbs’ principle of maximal entropy (and minimal energy) is the implicit expression of Clausius’ Second Law. In addition, by making explicit some implicit passages of Gibbs logical path, we provide an original formal justification of Gibbs’ principle. Finally we provide an analysis of how Gibbs’ principle—conceived for homogeneous isolated systems with fixed chemical composition—has come to be applied to systems entailing chemical transformations.