Publications

Abstract Monocrystalline gold surfaces having five different crystallographic orientations have been characterized by means of cyclic voltammetry in aqueous 0.11 M NaOH in order to examine the electrochemistry of oxide formation and removal in comparison with the well-characterized behavior in acidic media. For the higher-index faces Au(210) and (311), these voltammetric features in 0.11 M NaOH are closely similar to those observed in acidic electrolytes, although the occurrence of substantial OH- adsorption is signaled by a broad reversible current-potential feature at less positive potentials. For the low-index faces Au(100) and (111), however, the voltammograms in 0.11 M NaOH differ substantially from those in acid. These differences are ascribed to the influence of potential-dependent OH- adsorption, which overlaps with oxide formation and especially reduction, and attendant potential-induced surface reconstruction. The behavior of Au(110) is intermediate between that of these other two low-index and the higher-index faces. As for the voltammetric features in acidic electrolytes, such crystal face-dependent voltammetry in 0.11 M NaOH can be employed as a sensitive (albeit empirical) check of the chemical and physical state of the interface prior to other electrochemical measurements. © 1990.

Abstract The construction of a new Knudsen effusion apparatus for measuring vapour pressures of organic and organometallic solids as a function of temperature and the subsequent calculation of enthalpies of sublimation are described. The new apparatus enables the simultaneous operation of three different effusion cells, reducing, considerably, the time necessary for the study of each compound. The performance of the apparatus was checked by measuring, as a function of temperature, the vapour pressure of benzoic acid (between 307.15 and 314.15 K) and ferrocene (between 292.27 and 300.01 K), from which their standard molar enthalpies of sublimation, at 298.15 K, were derived: benzoic acid, Δcr gH298.15 XXX = 89.25±0.85 kJ mol-1; ferrocene, Δcr gH298.15 XXX = 72.39 ± 1.00 kJ mol-1. © 1990.

Abstract The standard (p^{o = 0.1 MPa}) molar enthalpies of combustion at 298.15 K were measured by static-bomb calorimetry and the standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry for phenazine, benzofurazan, and their corresponding N-oxides: {A table is presented}. From the standard molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies of the (NO) bonds werederived: D(NO)/(kJ · mol^-1): phenazine N-oxide, 280.7 ± 5.6; benzofuroxan, 250.9 ± 3.0. © 1990.

Abstract The standard enthalpies of formation of some crystalline copper(II) complexes were obtained from solution-reaction calorimetric measurements and the enthalpies of sublimation of Cu2(acetate)4, Cu(dmg)2 and Cu(PhNacac)2 were obtained from torsion-Knudsen vapour pressure measurements. The differences between the mean Cu-ligand and H-ligand dissociation enthalpies were derived and are given below. {A table is presented}. © 1990.

Abstract The specific heat capacity of the poly(ethylene glycol)-water system has been determined using a drop calorimeter over the full range of composition at 25 °C. The system heat capacity responds linearly to change in composition in the dilute solution regime up to 30% (w/w) and is an irregular function at lower water content. The breakpoint in solubility corresponds to a minimal content of 2.5 water molecules per ethylene oxide to complete hydration. We have difficulty in explaining the large excess heat capacity by the presence of a stoichiometrically defined hydrogen-bonded complex between each ethylene oxide group and water molecules. It seems possible that the water of hydration also interacts with bulk water and/or the rest of the polymer chain. © 1990.

Abstract The binding of a series of alkanediols, HO(CH2)NOH, n = 3 to 10, to α-cyclodextrin was studied by microcalorimetric titration at 288.15 K, 298.15 K, and 308.15 K. For n = 3 to 7, the results agreed well with a 1-1 binding model but for n = 8 to 10, a more complex stepwise-association model had to be assumed: the formation of both 1-1 and 1-2 (1 diol + 2 α-CD) complexes. Apparent values for the binding constants, and changes in the standard molar Gibbs energies, enthalpies, entropies, and heat capacities, were derived for the binding process. At all temperatures, enthalpy and entropy values show an initial zig-zag pattern as a function of the number of CH2 groups whereas the CH2 increment in the standard molar Gibbs energy change is regular up to C8. The heat-capacity increments are regular up to C6, after which they level off. The results are interpreted in terms of the expected "driving forces" leading to the binding and the observed pattern in the thermodynamic properties. © 1990.

Abstract The minimum in the differential capacity of (111), (100), (110), (210) and (311) single-crystal gold faces in contact with dilute solutions of HClO4 as a function of the temperature was used to estimate the temperature coefficient of the potential of zero charge of these interfaces. The results are discussed in terms of the interaction of water with the metallic surfaces and the role played by the surface atomic arrangement. The strength of Au (hkl)-water interactions are proposed to be in the order Au (111) > Au (311) > Au (100) > Au (110) > Au (210) ≈ Hg. © 1990.