Publications

Abstract The behaviour of two crystal faces of gold with extreme surface energies (111) and (210) in aqueous solutions of sulphamic acid was studied. The results indicate the influence of crystallographic orientation (c.o.) in the adsorption of sulphamic acid. The degree of adsorption is intermediate between perchlorate and sulphate, and is reflected on the oxidation process of gold single crystal faces. The results are interpreted in terms of the distortion of the trigonal structure of the anion. © 1989.

Abstract The standard molar enthalpies of formation, at 298.15 K, of five crystalline bent metallocenes, [M(η-C5H5)2L] (M = Mo, W, Ti) (LH2 = 1,2-benzenediol, C6H4-(OH)2; 2,3-napthalenediol, C10H6(OH)2; 9,10-phenanthrenediol, C14H8(OH)2), have been derived from enthalpies of hydrolyses in acid solution measured by precision solution-reaction calorimetry. The results were: ΔHf° [Mo(η-C5H5)2(O26H4),c] = -130.6±2.9, ΔHf°[Mo(η-C5H5)2(O2C10H6),c] = -80.3± 2.2, ΔHf° [ Mo(η-C5H5)2(O2C14H8,c] = -53.25 ± 10.4, ΔHf° [ W(η-C5H5)2 (O2C6H4),c] = -112.8 ±2.9, ΔHf° [Ti(η-C5H5)2(O2C14H8),c] = -322.6 ± 12.7 kJ mol-1. The metaloxygen bond strengths were evaluated as mean bond enthalpy terms (E). Comparison with corresponding values in similar comlexes reveals that small steric energy arises from the binding of a catechol type ligand to a metal atom. © 1988.

Abstract The standard (po = 101.325 kPa) molar enthalpies of combustion in oxygen at 298.15 K were measured by static bomb calorimetry for the two hydroxynaphthalenes and for four dihydroxynaphthalenes. The standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry for the 1,2-, 1,3-, and 2,3-dihydroxynaphthalenes. Literature values were used for the other compounds. The standard molar enthalpies of formation in the gaseous state were derived. {A table is presented}. The standard molar enthalpies of formation of the 1,2-, 1,3-, and 1,4-dihydroxynaphthalenes in the gaseous state follow the same pattern as those for the corresponding dihydroxybenzenes. © 1988.

Abstract The adsorption of mannitol and sorbitol was studied as a function of the bulk concentration. The degree of adsorption follows the order of the solubilities of the compounds. This result is explained by overriding solute-solvent interactions since the vertical interactions of both polyalcohols with the electrode surface are similar. The effect of temperature on the differential capacity and the derived entropy of formation of the interface corroborates the idea that a water structure different from that in the bulk is responsible for the discrimination in adsorption of the small structural differences between the two solutes. Some results obtained for another isomer of sorbitol, dulcitol, are in qualitative agreement with the model proposed. © 1988.

Abstract Enthalpies of combustion and vaporization and the heat capacity have been determined for glycerol at 298.15 K. Using microcalorimeter techniques, enthalpies of solution at infinite dilution have been determined for glycerol in water (288.15, 298.15, and 308.15 K). The partial molar heat capacity of glycerol in infinitely dilute aqueous solution was derived: Cp,2∞ = (239 ± 3) J · K-1 · mol-1. This value confirms the view that the special type of interaction with water found in higher polyhydroxyl compounds is still absent for glycerol. © 1988.

Abstract The gold (110)/perchloric acid interface was studied at temperatures ranging from 0.5 to 41° C by differential capacity-potential curves. The temperature coefficient of the Galvani potential drop was found to vary with the concentration of the solution, in contrast to what was observed for the (210) gold face. The azimuthal anisotropy and reconstruction of the gold (110) face make difficult interpretation in terms of a model of the variations of the entropy of formation of this interface. C1 (σ) curves with two round maxima were found. Comparison to result obtained with this gold face in KPF6 and the silver (110) face is discussed. The inner-layer capacity, at zero charge, for Au (110) in HClO4 is also discussed and the sign of its temperature coefficient is deduced from modified Parsons-Zobel plots. © 1987.

Abstract Quasiclassical trajectory calculations have been carried out for the Li + Na2 (ν = 0, J = 10) → LiNa + Na and Na + K2 (ν = 0, J = 10) → NaK + K reactions at collision energies of 3.5 and 2.3 kcal mol-1, respectively, using realistic potentials based on an extended-LEPS method. Most dynamics features suggest that those reactions proceed at such energies via an indirect mechanism. However, the analysis of the product internal state vibrational distributions show, particularly in the case of Na + K2, that it is not possible to assign a vibrational temperature to such distributions. The result from LIF experiments, which suggest a direct mechanism for Li + Na2 but are less conclusive for Na + K2, are thus only partly corroborated by the present calculations.

Abstract The temperature dependence of the differential capacity curves for the (210) gold face in perchloric acid solutions of concentrations ranging from 10 mM to 2 M has been examined. The temperature coefficients of the Galvani potential drops are almost the same as that of mercury in sodium fluoride. The variations of the inner layer capacity, as a function of the charge density, are discussed tentatively. The entropies of formation of the interface and of the inner part of the double layer, as a function of the charge density, are reported. © 1987.

Abstract In the presence of "inert" electrolytes (sodium fluoride, sulfate, carbonate, phosphate) there exists a range of temperatures and thiourea (TU) concentrations (low and high respectively) where two distinct condensed TU monolayers, totally devoid of anions, are observed. The two relevant molecular structures which are suggested rest on the analysis of the following data: (1) E-T-[TU] phase diagrams derived from capacitance measurements, (2) superficial excesses and molecular areas, (3) charge densities, (4) inhibition power, and (5) kinetics displayed by the various phase transitions involved. Anions like ClO- 4, NO- 3, ClO- 3 are only coadsorbed within the gas-like film of TU, with the result that the pure TU condensed regions are squeezed detectably. On the other hand, anions known to interact strongly with Hg (Cl-, Br-, I-, SCN-)_do coadsorb significantly at all potentials. However, pure TU films tend to reappear if the concentration of these anions is lowered sufficiently with respect to that of the surfactant. © 1987.