Photocurrent kinetics at electron emission from metal to electrolyte solution: Part V. Ionization rate constants of hydrogen and deuterium atoms adsorbed on mercury

Absolute ionization rate constant values of hydrogen and deuterium atoms adsorbed on mercury were measured using the method of pulse photoelectronic emission from metal into solution. In accordance with the Tafel law, these constants decrease from 2.5×10⁷s^?1 to 9×10⁵s^?1 (Table 1) in a 1 M solution of KCl in the range ?0.25 to ?0.5 V SCE. The transfer coefficient is 0.33±0.03 and the isotope ratio about 2.5. Owing to specific anion adsorption, rate constants increase as their concentration increases and KBr is added to the solution. In 0.05 M solutions of HCl and H₂SO₄, transfer coefficients are 0.30±0.05. From a comparison of measured values, with the hydrogen ion discharge rate constants found by extrapolation of experimental values into the potential range mentioned (taking into account the transfer coefficient change), the change of the Gibbs free energy in the reaction H₃O⁺+e_Me^?→H_ads+H₂O was calculated and found to be 0.87–0.99 eV at the potential of the normal hydrogen electrode. Adsorption energy of the hydrogen atom from the gas phase on a mercury electrode is 1.55±0.10 eV.The volt-ampere dependence of the hydrogen ion discharge current in the range ?0.25 to ?2.25 V corresponding to the current change by 18 orders of magnitude, agrees with the theoretically determined values (maximum deviation in the current is less than a factor of 3) for the medium reorganization energy E_r=1.75 eV. Despite constancy of the transfer coefficients of the elementary stages, in the range ?0.5 V (SCE), the effective transfer coefficient of the total hydrogen evolution processes increases from 0.5 to 1.0, as the ionization rate of the adsorbed hydrogen atoms becomes greater than their electrochemical desorption rate.     

Synthesis of 3-R2-4-R1-acetyl-(ethoxycarbonyl)-6-hydroxy-6-methylindazoles

It was discovered that functionally substituted tetrahydroindazoles can be aromatized by the action of sulfur. Previously unknown 3-R²-4-R¹-5-acetyl(ethoxycarbonyl)-6-methylindazoles were obtained. The products from aromatization cannot be obtained if a nitro group is introduced or one heteroatom in the substrate is replaced by oxygen.N. G. Chernyshevskii Saratov State University, Saratov, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 757–759, June, 1999.     

Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.     

Photovoltaic properties of polymeric ferroelectric with various dopings

The photovoltaic properties and the bulk photovoltaic effect have been studied in a polyvinylidene difluoride–trifluoroethylene polymeric ferroelectric doped by single-walled nanotubes and a ruthenium-based dye. The dopants serve as spectral sensibilizers that improve sensitivity to 532-nm laser radiation.     

Bipolar Electrochemical Exfoliation of Graphite for Synthesizing Electrocatalysts of Oxygen Reduction

Russian Journal of Electrochemistry - A nanocomposite of few-layer graphene structures with cobalt oxides is synthesized for the first time in an aqueous electrolyte containing Co2+ ions by the...     

Binuclear Robson type Ni(ii) complex as a reactant supplementing our knowledge of the orientation effects in electrochemical kinetics

The multistep reduction of a binuclear Ni(ii) Robson-type complex with a multidentate template-like organic ligand (formed from 4-tert-butyl-2,6-diformylphenol and 1,3-diaminopropane), Ni(2)L, is studied using the electron photoemission technique. The number of transferred electrons corresponding to a single reduction wave is found to be 8 per complex species. This value is attributed to both complete Ni(ii) reduction (with Ni metal formation) and ligand reduction. Contributions of Ni(ii) and ligand to acceptor orbital were estimated. Three initial subsequent steps correspond to electron transfer to mixed metal-ligand orbital with comparable contributions. For more deep reduction, ligand contribution predominates. The first single-electron step is evidenced to be rate-determining, with the rate constant of 0.03 cm(2) s(-1). The latter value is discussed in the framework of a semiquantitative analysis of the rate constants estimated in the framework of quantum-mechanical electron transfer theory for different orientations of Ni(2)L in the reaction layer. The analysis includes estimations of key kinetic parameters (electronic transmission coefficient, solvent- and intramolecular contributions to the total reorganization energy) which strongly rest on the results of quantum chemical modeling. The transmission coefficients at realistic electrode-reactant distances of the closest approach are below 0.001. This means that despite of the noticeable delocalization of Ni(2)L acceptor orbital, the electron transfer is diabatic. Predominating contribution to reorganization energy results from solvent and does not exceed 0.5 eV for any reactant orientation. The highest reactivity is predicted for a planar orientation located mostly outside the compact part of electric double layer. The Ni(2)L adsorption in planar and vertical orientations on mercury is addressed as well. The results give a clear explanation of the previously observed self-inhibition of "dark" reduction of Ni(2)L on mercury and independent data on the adsorption of these species. The discovered combination of various orientation effects is compared with effects observed for other reactants.