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The charge-transfer reaction between copper͑II͒ and copper electrodes is studied in electrolytes that are similar to galvanic copper baths, 2.2 M H 2 SO 4 ϩ 0.3 M CuSO 4 ϩ chloride ions (c Cl р 1 ϫ 10 Ϫ2 M͒, and polyethyleneglycol 1500 ͑PEG, c PEG р 4 ϫ 10 Ϫ3 M͒. Electrochemical quartz crystal microbalance ͑EQCM͒ measurements are conducted, mainly under conditions of cyclic voltammetry. The formation and dissolution of CuCl on the electrode surface at c Cl у 2 mM is demonstrated, a notable shift of the pseudo-equilibrium potential associated with CuCl deposition is analyzed, and the inhibition of the charge-transfer reaction by the PEG/Cl Ϫ surface layer is characterized. It is shown that the inhibiting layer forms by reaction between the adsorbate-covered copper electrode and PEG, i.e., neither Cu ϩ nor Cu ϩϩ from the electrolyte are required. Numerical simulations of the processes as well as parallel experiments conducted with electrolytes not containing Cu͑II͒ support the proposed mechanisms, in particular the role of the intermediate Cu ϩ .

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Electrochemistry / Copper / Halides / Mechanism / Electroplating / ElectrorefiningThe cathodic reduction of copper(II) in an electrolyte comparable to technical conditions (2.2 M H 2 SO 4 + 0.3 M CuSO 4 ) is markedly affected by the presence of small concentrations of halide ions. Chloride ions accelerate the reaction, while it is slowed down by bromide. Experiments in which cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface. At the technically relevant more negative electrode potentials bulk CuCl and CuBr are unstable, however halide ions are adsorbed on the copper electrode. Although there is evidence for adsorption of the reacting Cu(II) species at the electrode surface, up to a concentration of 0.3 M CuSO 4 in presence as well as in absence of adsorbed halogenide, there is no evidence for limiation of the reaction rate caused by a limited coverage of the surface with this species.

A quartz oscillator, operated with one of its faces in contact with a liquid, can be used as a highly sensitive microbalance. When used together with an electronic driver circuit, frequency changes will not only reflect changes of vibrating rigid mass but also detect changes of the surface microstructure. Using impedance spectroscopy we have analyzed the influence of the surface microstructure on the frequency changes. A liquid that is rigidly coupled to the surface by inclusion into voids or narrow channels can be discerned from a liquid that is viscously coupled to the surface. This analysis is shown for silver surfaces, roughened by several oxidation and reduction cycles, in chloride ion containing solutions.

We use a vector analyzer to investigate the impedance of a quartz oscillator, one face of which is exposed to a liquid. An aqueous LiCl – solution can be used to vary density and viscosity of the liquid over a wide range. The solution acts as an additional impedance with as well a real as an imaginary part. Furthermore, different electrical driver circuits have been used to excite the crystal vibrations. In most cases, our experimental results deviate from the predicted dependence of the crystal frequency from density and viscosity. These deviations are different for different driving circuits, but they do not change with the properties of the liquid.

Rates were measured for the association of CO, CH4, CH3F, NH3, ND3, CH3Cl, and CH3Br onto Ag+ and Cu+ at 298 K. In the order given above, the three-body association rate constants for Ag+ range from 2.5×10−30 to 3.9×10−27 cm6 s−1. The rate constants for Cu+ are about four to six times larger for a given neutral reactant. The rate constants display trends in the order expected considering the relative bond energies of the clusters, although the enormous range of reactivity is not reflected simply by differences in dipole moments and polarizabilities. There is a very large isotope effect, where the rate constant for ND3 association was found to be about three times greater than NH3 in the case of both ions. (Results for Na+ follow the same trend.) This suggests a coupling of ligand vibrations with orbiting motion which leads to enhanced lifetimes of the cluster intermediates. The trend found for the methyl halides also supports the involvement of this effect.

An experiment with five steps within a mass spectrometer (labeled MSn) showed that in the gas phase the naked Fe 4+ ion forms the molecule C6H6, probably benzene, from ethene via [Fe4(C2H2)m]+ complexes (m = 1–4), and thus acts as a catalytic center. The MS1–MS5 steps of the complex experiment are sketched below. CID = collision‐induced deactivation, a = isolation, m = 1–3.