J. Virgili

Potentiostatic reversible reaction when both reactant and product are adsorbed at the dropping mercury electrode: Part I. Theoretical treatment

Abstract The theoretical treatment of diffusion-limited, reversible electrode reactions with adsorption of reactant and/or product of the reaction under potentiostatic conditions, developed by Reinmuth and Balasubramanian in 1972, is extended, thus permitting the study of adsorption isotherms of the more usual kind (Langmuir, Frumkin, etc.) as well as other more complex types (e.g. multilayers, experimental isotherms…). Moreover, exact general equations in the form of faradaic instantaneous current vs. time and average current vs. potential (the polarographic curve) have been obtained. Nowadays computational techniques easily provide a numerical solution for these equations. The classical approximations proposed to obtain analytical expressions for these equations can be easily deduced from the general equations obtained in this paper, thus giving a general frame for these approximations. Their accuracy is also discussed.

A simple modification of the LEPS surface suitable for the ion—molecule processes Az+ + BB → Az+ + BB, ABz+ + B

Abstract On electrostatic arguments we propose a simple modification of the LEPS surface, specially suitable for the theoretical study of the ion—molecule processes Az+ + BB → Az+ + BB, ABz+ + B in the gas phase. The new surface has been used to fit the 1 2Σ+, 1 2Π, 1 2A′ and 2 2A′ CH+2 potential energy surfaces, showing a much better fit than the LEPS surface, particularly in the case of the potential energy surfaces with a minimum between reactants and products (1 2Π and 1 2A′).

Potentiostatic reversible reaction when both reactant and product are adsorbed at the dropping mercury electrode: Part II. Langmuirian and Frumkinian adsorption

Abstract Following the treatment developed in Part I to study reversible reactions with adsorption of the reactant and/or product of the reaction under potentiostatic conditions, we particularize such treatment in the case of Langmuirian and Frumkinian adsorption, with the aim of solving numerically the proposed system of equations. Thus, a comparison is made between results obtained by this method and by approximate methods found in the literature. A study of the parametric dependence of the general equations for Langmuirian adsorption has also been carried out.

Activity coefficients of aqueous perchloric acid

Mean ionic activity coefficients for aqueous perchloric acid at 25°C were obtained from the emf of a HClO4 concentration cell (m=1×10−3−1.5) containing a ClO4− ion solution electrode and a glass electrode. The results of an application of the Pitzer equations are compared with those previously reported from several different measuring methods. Perchloric acid activity coefficients have been calculated for the mixture HClO4−NaClO4. In both cases, good agreement has been obtained between our results and those derived from the isopiestic method.

Dissociative chemisorption of molecular hydrogen on graphite: A mindo /3 study

Abstract The dissociative chemisorption of molecular hydrogen on graphite has been studied using a small cluster to represent the graphite surface. Calculations were carried out using the UHF and RHF (including configuration interaction) versions of the MINDO/3 program. Results show that geometry optimization is necessary and that the choice of the reaction coordinate is of major importance. Dissociative chemisorption is predicted and a potential barrier is found. Results are in agreement with the molecular beam experimental data in the literature.

Potentiostatic oxidation of aluminium in propanedioic and sulphuric acid solutions

Abstract The potentiostatic behaviour of a 99.9995% aluminium electrode in 0.05, 0.10, 0.50 and 1.00 M propanedioic acid and in pH = 1.00 sulphuric acid solutions, at potentials in the range 1.00–5.00 V vs sce has been studied. At their beginning, the experimental curves show a marked current density decay with time; subsequently, a minimum, a maximum and a steady-state current density are found, proving the occurrence of a porous evolution. The study of the current density decay region, by applying the kinetic equations for charge transfer, metal dissolution and ionic migration, gives evidence of oxide formation with a certain inefficiency of growth. In the early stages of the potentiostatic oxidations, the results are in agreement with Chao, Lin and Macdonalds model on ionic migration and with the Al3+ ejection at the film/electrolyte interface that has been recently suggested from O18 tracing techniques and electronoptical data.

Quasiclassical trajectory study of the ion—molecule reaction C+(2P) + H2(X 1Σ+g) → CH+ + H near the threshold energy

Abstract In our recent work on the C + ( 2 P)+H 2 → CH + + H reaction, we did not consider a recent experimental cross section that disagrees with our calculated value. A simplified evaluation of a diabatic contribution to the reaction shows its magnitude to be very small. We think that the discrepancy is mainly due to the fact that the PES we used is too repulsive.

Anodic behaviour of a mercury electrode in aqueous 8-hydroxyquinoline solutions☆

Abstract Anodic dissolution of the hmde from 8-hydroxyquinoline (Ox) aqueous solutions at pH = 5.2 is attributed to the formation of insoluble organomercuric derivatives. The experimental results show that the process happens in two steps. The first one takes place with adsorption of electroactive species, while an insoluble product, which can produce the inhibition of the electrode process, is formed in the second one.

Polarographic and voltammetric studies of 8-hydroxyquinoline and 8-hydroxy- 5-quinolinesulfonic acid in aqueous solutions—basic media

Abstract We have compared the polarographic and voltammetric behaviour of 8-hydroxyquinoline and 8-hydroxy-5-quinolinesulfonic acid in buffered aqueous solution at basic pH. The results let us consider the process of dimerization of the radical formed in the first electrode step for both compounds, although they follow a different mechanism. The reduction of the radical derived from 8-hydroxy-5-quinolinesulfonic acid is competitive with its dimerization at cathodic enough potentials. The characteristics of reduced compounds are consistent with the electrochemical schemes proposed.

MINDO/3 study of periodic overlayers on graphite

Abstract The crystalline orbital MINDO/3 method has been applied to the study of regular phases of H, C, N, and O chemisorbed on graphite. Results for regular phases of H are comparable to ab-initio band calculations. While band structures are similar topologically to available CNDO/2 data, the MINDO/3 method overcomes the main deficiencies of CNDO/2 and EHT approaches, not needing either the introduction of scale factors on the calculated energies or the manipulations on the parametrization. For atomic H, C and N phases, the stablest one corresponds to a 1:1 composition, while for atomic O it corresponds to a 1:2 surface composition. The band structure of each one of the stablest phases is discussed and the results are compared with previous MINDO/3 cluster model calculations.