Thermal energy charge transfer reactions of acetone and biacetyl

Rate coefficients up to a factor of 2.5 times larger than the capture collision rate are reported for a series of thermal energy, positive ion-molecule reactions of acetone and biacetyl. These rapid rates are interpreted in tems of a dissociative charge transfer process in which an electron is transferred in a non-spiralling collision from outside the classical capture limit. The factor which lead to this type of mechanism are discussed briefly.     

Effect of electron-electron correlations on the activation free energy of adiabatic electrochemical reactions of dissociative electron transfer

Adiabatic free energy surfaces for adiabatic electrochemical reactions of dissociative electron transfer are calculated with exact allowance for the effects of electron-electron correlations in a model of an electrode with an infinitely broad conduction band. The role of correlation effects in these reactions is discussed. It is shown that, as in common adiabatic electrochemical reactions of electron transfer, correlation effects play a substantial role and lead to a considerable decrease in the activation free energies.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 412–418.Original Russian Text Copyright © 2005 by Kuznetsov, Medvedev, Sokolov.     

Catalysis of slow charge transfer reactions at polypyrrole-coated glassy carbon electrodes

Oxidation of ascorbic acid, dihydroxyphenylacetic acid and dopamine are compared at polypyrrole-coated glassy carbon and naked glassy carbon electrodes. These currents are mass-transport limited and not limited by permeation into or through the polypyrrole film. Ascorbic acid oxidation occurs at potentials 300 mV more negative at polypyrrole-coated electrodes and the rising slope of rotated disk voltammograms changes by over 100 mV. A similar enhancement in electrochemical reversibility is observed for dihydroxyphenylacetic acid, whereas dopamine is oxidized at slightly more positive potentials at polypyrrole-coated electrodes. Comparing the electrochemistry of dopamine and dihydroxyphenyl-acetic acid, it appears that the electrochemical reversibility differences for these substances are to some degree result of electrostatic interactions between the anionic solutes, or anionic reaction intermediates, and anionic functional groups on carbon or cationic fixed sites in oxidized polypyrrole.     

电化学方法用于分子内电荷转移特性的研究

设计合成一系列具有不同取代基的苯甲酰萘（苯）胺衍生和，测定它们在非极性溶剂环己烷中的荧光发射光谱，发现系列合成产物具有双重荧光，其长滤发射具有电荷转移特性，其长波发射态能量与不同取代基的苯甲酰萘（苯）胺衍生物的失（得）电子能力，即给（受）体的氧化还原电位之间符合Weller方程。     

A Born-Oppenheimer approach to adiabatic electrochemical charge transfer processes

An approach for the construction of the Hamiltonians and free energy surfaces for adiabatic electrochemical reactions accompanied by a considerable reorganization of the intramolecular structure is presented. For one-electron processes it reproduces the results of Koper and Voth (Chem. Phys. Lett. 282 (1998) 100) without an a priori introduction of a switching function transforming the bonding molecular potential into an antibonding one. The present approach is extended to two-electron processes, which are of importance for the dissociative adsorption and electrocatalysis.     

Photoinduced energy transfer and charge transfer on squarylium cyanine dyes

A series of squarylium cyanine dyes (Sqs) were synthesized to explore their applications in functional devices.Preliminary investigation on the mechanism involved in these devices was carried out.Spectroscopic behavior of Sqs with porphyrin (P),8-hydroxyquinolium aluminum (Alq) and ruthenium bipyridyl complex (Ru(bipy)) in solution,in film and on nanocrystalline TiO2 was investigated,respectively.A mechanism including photoinduced energy transfer and charge transfer processes was suggested in the corresponding practical devices.By means of doping,a red organic electroluminescent device (ELD) using Sq-doped Alq as the emission layer (EML) has been developed,and the total light to electricity efficiency of nanocrystalline TiO2 electrode based on using Sq-doped Ru(bipy) as photosensitizer has been improved greatly in the whole visible region,particularly in the red area above 600 nm.     

Actual activation energy of electrode process under mixed kinetics conditions

In the case of a single-electron reaction with account for slow diffusion of reagents, equations for actual (experimentally determined) activation energies of two types were derived and analyzed: real energy A f, i.e., the energy measured at a constant electrode polarization value η = const) and formal energy (Ω_f, i.e., the value measured at a constant value of potential vs. an ambiguously chosen reference electrode E = const). It is found that under the conditions of a sufficiently significant deviation from equilibrium, the actual activation energy A _f is the weighted arithmetic mean of the diffusion activation energy and the sum of A ₀ + αFη (where A ₀ is the real activation energy of the discharge stage at polarization of η = 0); herewith, the weighting coefficients are the corresponding values of the current of the discharge stage and the limiting diffusion current. A similar relationship is also obtained for Ω_f. It is found that the A _f, η- and Ω_f, E-curves can in a number of cases feature regions with the negative A _f and Ω_f values in the mixed kinetics range.     

Sensitivity of charge transfer reactions to hydrocarbon ion structures

Charge transfer reactivities of hydrocarbon ions have been measured with time-of-flight techniques, and results correlated with theoretical structures computed by self-consistent field molecular orbital methods. Recombination energies, ion structures, heats of formation, reaction energetics and relative charge transfer cross-sections are presented for molecular and fragment ions produced by electron bombardment ionization of CH₄, C₂H₄, C₂H₆, C₃H₈ and C₄H₁₀ molecules. Even-electron bridged cations have low ion recombination energies and relatively low charge transfer cross-sections as compared with odd-electron hydrocarbon cations.     

Thermal energy charge transfer reactions of Ar+ ions with HBr and DBr molecules

HBr⁺ (A²Σ⁺-X²Π_i) and DBr⁺ (A²Σ⁺-X²Π_i) emissions are found up to v′=1 and v^′=2, respectively, from the thermal energy charge transfer reactions of Ar⁺ with HBr and DBr molecules in a flowing afterglow apparatus. Both A-state vibrational distributions have a peak at the lowest vibrational level, which are inconsistent with those expected from the energy resonance and/or Franck-Condon factors for ionization. This discrepancy is explained in terms of the distortion of target molecules by approach of reactant ions. Both A-state rotational distributions show that energies partitioned into rotation decrease with increasing vibrational levels, whereas the internal energy is nearly constant for all vibrational levels. The vibrational and rotational distributions obtained suggest that the reaction occurs at a relatively short distance and the product has a broad translational energy distribution.     

Ionic components dependence of the charge transfer reactions at the silicon/HF solution interface

The actual requirements for circuit miniaturization and production economy require obtaining smooth silicon surfaces using diluted chemicals, especially HF treatment. This fundamental research deals with the electrochemical corrosion of n- and p-type silicon substrates in 0.25 M dilute HF solutions, and examines the influence of fluoride ions or protons additives. All experiments were conducted both in the dark and under constant light flux, with solutions thoroughly degassed by high purity argon bubbling. Polarization resistance measurements near the open circuit potential lead to the value of the corrosion current. The kinetics of charge transfer reactions, studied by linear voltammetry, were interpreted as a function of the carrier density in the energy levels of the semiconductor and the concentration of acceptor species in the solution. The influence of these parameters on the surface roughening of the silicon samples was also studied by ex situ atomic force microscopy profile measurements. Received: 13 December 1998 / Accepted: 29 March 1999     

The effect of partial charge transfer on the electrochemical turbulent noise

Theoretical analysis of the effect of electrode potential on the spectral density of random alternating current emerged in electrochemical cell under the action of turbulent pulsations of the electrolyte solution velocity is carried out. An impedance model of metal electrode dissolution reaction, including two adsorption stages, is suggested, with allowance for the oxidized ion diffusion in electrolyte solution. It is known that in terms of the Ershler-Randles model, at low frequencies the experimentally measured slope of bilogarithmic frequency dependence of spectral density equals 3, which is characteristic of the diffusion control; at high frequencies the slope equals 4, which is characteristic of the kinetic control. It is shown that for the model of impedance of the two-stage adsorption oxidation process, in the middle segment of the spectrum the local slope must decrease down to 2, provided the first oxidation stage, which proceeds within the inner electrical double layer, is slow; the local slope must increase up to 6 (or 5, for diffusion control), provided the second oxidation stage (the partially oxidized ion desorption to solution) is slow. The “height” and “width” of the slope local changes appeared explicitly depending on the parameters of the partial charge transfer. This makes the turbulent noise method somewhat superior to the impedance method in the studying of the above-specified reaction type.     

Intramolecular energy transfer reactions in polymetallic complexes

A series of polymetallic complexes are being developed for use in converting solar radiation to usable chemical potential energy. The system is made up of three components: 1) A highly-absorbing (antenna) metal center which absorbs visible light but is photochemically unreactive; 2) A second metal center which undergoes a useful chemical reaction from a non-spectroscopic excited state; and 3) A bridging ligand which couples the two metal fragments and facilitates intramolecular energy transfer from the antenna to the reactive fragment. This paper will focus on optimizing the three components of the system.     

Some charge transfer reactions of excited aromatic compounds with sulphides

Photo-reductive dehalogenation of aromatic halides to their parent hydrocarbons is stimulated in the presence of electron donors such as di-ethyl sulphide. Evidence is presented for the involvement of radicals ions in these reactions.     

Mass transport at electrodes of arbitrary geometry. Reversible charge transfer reactions in square wave voltammetry

The basis for mass transport of the electroactive species in different diffusion fields is examined, pointing out important insights in relation to the value of the surface concentrations for the case of fast electrode processes. Moreover, a general analytical solution for the transient current is given for several geometries, when an arbitrary sequence of potentials pulses is applied to macroelectrodes (planar), spheres, cylinders, discs and bands. The results are particularized for Square Wave Voltammetry. Explicit solutions for the net current and the forward and backward components are given. The effects of frequency, pulse amplitude and electrode size or shape on the peak current are studied. Moreover, the conditions for the attainment of the steady state response are analyzed in the different geometries as well as the characteristics of this response.