Experiments on solvated electron generation and deposition in hexamethylphosphoramide

Theory is developed and compared to experiment for the cyclic voltammetric ejection and redeposition of solvated electrons e_s^? in NaClO₄ and LiCl solutions in HMPA. In current reversal chronopotentiometry, e_s^? mass transfer can be observed free from uncompensated resistance effects by cathodic generation of e_s^? for time t_f followed by anodic current redeposition leading to a reverse transition time τ_b. The ratio τ_b/t_f depends on t_f, applied current, and LiCl electrolyte concentration. Comparison of τ_b/t_f to theory detects a highly reactive scavenger at micromolar concentration levels.     

ESR of O− and O2− stabilized on95Mo ions in a molybdenum-silica gel support system

The O^? and O₂^? anion radicals adsorbed at surface molybdenum ions were investigated by the EPR method by using the⁹⁵Mo isotope. From the valuesg_∥ = 2.006,g= 2.021,a_∥ = 7.6G anda= 8.0G for the O^? anion-radical the unpaired electron density (≈2%) was calculated. It is concluded that the unpaired electron in O^? is also delocalized onto the lattice oxygen ions.     

Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Hemoglobin (Hb) and silver–silver oxide (Ag–Ag₂O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H₂O₂) at co-immobilized electrodes showed a linear relationship with H₂O₂ concentration over a concentration range from 6.0?×?10^?6 to 5.0?×?10^?2 mol L^?1, and a detection limit of 2.0?×?10^?6 mol L^?1 (S/N?=?3).     

The geometric, energetic, and electronic properties of charged phosphorus-doped silicon clusters, PSi n +/PSi n ? (n?=?1�C8)

Charged phosphorus-doped small silicon clusters, PSi _n ⁺/PSi _n ^? (n?=?1?8), have been investigated using the B3LYP/6-311+G* level Kohn?CSham density functional theory (KS-DFT) method. For comparison, the geometries of neutral PSi _n clusters were also optimized at the same level, though most of them have been previously reported. According to our results, cationic PSi _n ⁺ clusters have ground state structures similar to those of pure silicon clusters Si _n+1, with the exception of n?=?5. For anionic PSi _n ^?, most of the lowest-energy structures are in accord with Wade??s 2N+2 rule for closed polyhedra: PSi₄ ^?, PSi₅ ^?, PSi₆ ^?, and PSi₈ ^?, respectively, favor the trigonal bipyramid, tetragonal bipyramid, pentagonal bipyramid, and tricapped trigonal prism (TTP) structures, corresponding to Wade??s 2N+2 rule with N?=?5, 6, 7, and 9. The structures tend to contract when the cationic species is reduced initially to the neutral species and subsequently to the anionic species, implying a strengthening interaction between atoms within the clusters on one and two electron reductions of the cationic species to the neutral and anionic species, respectively. The relative order of stability of the PSi _n ⁺/PSi _n ^? isomers differs from that of the PSi _n isomers. Cluster stability was also analyzed by adiabatic ionization potentials (AIP), adiabatic electron affinities (AEA), binding energies (BE), second-order energy differences (?₂E), and HOMO-LUMO gap values. The results indicate that PSi₄ ^? and PSi₇ ^? clusters are more stable than their neighboring anionic clusters and would be potential species for further mass spectrometric measurements.     

Ion-Molecule reactions in methylamine and dimethylamine and trimethylamine systems

Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH₃NH ₃ ⁺ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10^?10 and 9.3 ± 0.9 × 10^?10 cm³ molec^?1s^?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH₃NH ₂ ⁺ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10^?10 and 15.0 ± 5 × 10^?10 cm³molec^?1s^?1, respectively.     

Ab-initio study of localization of an excess electron in sodium halide clusters

The equilibrium geometries of Na _n F _n and Na _n F _n?1 are optimized forn=2, 3, 4 at the SCF level. The Na _n F _n molecules appear as formed by Na⁺ and F^? ions. The paper studies the localization of the excess electron in the Na _n F _n?1 molecules. Na _n F _n?1 is obtained by removing from Na _n F _n a fluorine atom, and the excess electron takes the place of this lacking center, and allows a weak bond between the neighbouring Na atoms. Secondary minimum geometries, for which the excess electron has no defined place, are also studied.     

Electrochemical and kinetic study of oxygen in a perfluorotributylamine emulsion

Oxygen can be determined in a perfluorotributylamine emulsion used as a blood substitute by coulometry and polarography. The oxygen uptake of the emulsion (4.3 × 10^?3 mol l^?1 or 11 ml-% at 25°C and P_O2 = 760 mm Hg) is about three times greater than that of water. The adsorption of surfactant on a dropping mercury electrode changes the electrochemical parameters E_{$\text{1}\text{2}$}, α and k₃. The marked difference between the diffusion coefficients of oxygen and hydrogen peroxide (ratio 2.6) seems to be proceed from the ejection of oxygen molecules from the perfluorotributylamine droplets and from the insolubility of hydrogen peroxide molecules in the droplets. The constant rate of oxygen release by these droplets was estimated to be 10⁴ s^?1 by a stopped-flow spectrophotometric method. This constant rate seems to be linked with the particle diameter (0.2 μm) and the diffusion coefficient in the perfluorotributylamine droplets (1.6 × 10^?6 cm² s^?1).     

Relativistic theory forK-shell ionisation by fast electrons

The first-order Born approximation is applied for the calculation of the triply differential cross section for electron ejection from heavy target atoms. For the impinging electron, Coulomb waves as well as plane waves are used, and the exchange interaction is correctly accounted for. Two examples are considered,e ^?+Ag ande ^?+Ta. While for Ag, reasonable agreement with the experimental spectra is obtained with plane waves, the much heavier Ta target requires the use of Coulomb waves for the continuum electronic states.     

Spin exchange in low energy electron-ion collisions

The elastic scattering of an electron by a hydrogenic ion of charge (Z-1) is investigated. For scattering energiesE _kin in the eV region, where the Bohr-Sommerfeld parametery is large compared to one, the cross section for spin exchange of the electrons is found to be proportional toZ ^?2 andE ^?1 _kin. Spin exchange is dominated by radiative electron capture forZ>25.     

Secondary reactions in controlled potential coulometry: Part V. Reversal coulometric study of the reduction of cis- and trans-thioindigo in the presence of carbon dioxide,cinnamonitrile and acrylonitrile

Controlled potential reversal coulometry was applied to the following systems: (I) C+neR; R+C → RC; RC+ne → products. (II) as in (I) except RC not electroactive. (III) C+neR; R+X → RX; RX+ne → products. Equations for these e.c.e. and e.c. mechanisms were obtained and solved numerically. Working curves are presented for the calculation of the rate constants of the homogeneous reactions. This treatment was applied to studies of the reduction of thioindigo (TI) alone and in the presence of several reactants. For TI alone the reaction mechanism involves reaction of the radical anion (TI^?_·) with parent molecule followed by a second electron transfer. In the presence of excess dissolved CO₂, acrylonitrile (AN), or cinnamonitrile (CN), reaction of TI^?_· with these followed by a second electron transfer was proposed. Rate constants for the TI?TI^?_· coupling reaction were 82 (cis-thioindigo), and 323 (trans-thioindigo) l mol^?1 s^?1; pseudo-first-order reactions of TI^?_· were 0.016 (trans-) and 0.047 (cis-) s^?1 with CO₂; 0.023 (trans-) and 0.033 (cis-) s^?1 with CN; 0.022 (trans-) and 0.032 (cis-) s^?1 with AN.     

Ab-initio study of Na n F n and Na n F n−1 clusters: atypical structures

Alkali halide clusters Na _n F _n have most frequently cuboid structures and Na _n F _n?1 clusters are derived from Na _n F _n by removing a F^? centre. An excess electron localises on the site of the removed F^? ion. In this paper, other kind of clusters are studied at the SCF level: i) The non-cubic structures. ii) The cubic Na _n F _n?1 for which the excess electron has no defined site. Due to very large size of these species (at least 27 atoms!) some equivalent fictive linear and planar geometries are studied.     

Quantum chemical DFT calculations of the local structure of the hydrated electron and dielectron

The adiabatic bound state of an excess electron is calculated for a water cluster (H₂O) ₈ ^? in the gas phase using the DFT-B3LYP method with the extended 6-311++G(3df,3pd) basis set. For the liquid phase the calculation is performed in the polarizable continuum model (PCM) with regard to the solvent effect (water, ? = 78.38) in the supermolecule-continuum approximation. The value calculated by DFT-B3LYP for the vertical binding energy (VBE) of an excess electron in the anionic cluster (VBE(H₂O) ₈ ^? = 0.59 eV) agrees well with the experimental value of 0.44 eV obtained from photoelectron spectra in the gas phase. The VBE value of the excess electron calculated by PCM-B3LYP for the (H₂O) ₈ ^? cluster in the liquid phase (VBE = 1.70 eV) corresponds well to the absorption band maximum λ_max = 715 nm (VBE = 1.73 eV) in the optical spectrum of the hydrated electron hydr e _hydr ^? . Estimating the adiabatic binding energy (ABE)e _hydr ^t- in the (H₂O) ₈ ^? cluster (ABE = 1.63 eV), we obtain good agreement with the experimental free energy of electron hydration ΔG ₂₉₈ ⁰ (e _hydr ^? ) = 1.61 eV. The local model (H₂O) ₈ ^2? of the hydrated dielectron is considered in the supermolecule-continuum approximation. It is shown that the hydrated electron and dielectron have the same characteristic local structure: -O-H{↑}H-O- and -O-H{↑↓}H-O-respectively.     

A Study of picosecond dehalogenation of chlorobenzene anions in liquids by positronium inhibition measurements

Radiation chemistry and results of Ps yields indicate that the following processes occur in the positron spur in solution of halogen-substituted hydrocarbons, RX_n: e⁺ + e^? → Ps, e^? + RX _n → (RX_n)^? → RX_n?1 + X^?, e⁺ + (RX_n)^? → Ps + RX_n, e⁺ + X^? → [X^?, e⁺]. Hence the trapped electron can form Ps only if (RX _n)^? is stable or has a lifetime that is longer than o comparable to the Ps formation time. Previous studies have shown that some of the strongly chlorinated benzenes (n = 4.5 give reasonable inhibition in benzene but not in linear hydrocarbons. The reason is very probably that the dechlorination time is much shorter in benzene than in saturated hydrocarbons because Cl^? is more strongly solvated in benzene than in non-aromatic hydrocarbons. To test those ideas further we have begun detailed studies of solutions of the possible “intermediate” inhibitors, viz. 1,2,3,5- and 1,2,4,5-C₆H₂Cl₄, in mixtures of C₆H₆/C₆H₁₄ different methyl-substituted benzene aniline, anisole, dioxane and ethylbenzene. The results are discussed and interpreted in terms of the spur model. The Ps inhibition efficiency of the two isomeric forms of tetrachlorobenzene studied, appears most probably to depend on intramolecular electron transfer with subsequent dehalogenation of the molecular anion on a picosecond timescale. The divergence in inhibitor efficiency obtained for the chlorobenzenes when dissolved in aromatic solvents compared to the same solutes when dissolved in a saturated alkane appears most probably to be caused by complex formation between the initially formed chlorobenzene anion and benzene molecules, which permits a rapid relaxation of the molecular anion with subsequent bond stretching and expulsion of the chloride anion.     

Pulsed radiolysis of perrhenate in neutral aqueous solution: Comparison with pertechnetate

Reaction of perrhenate with the aquated electron in neutral aqueous solution yields ReO₄^2? (k_f 1.3 × 10¹⁰ M^?1 s^?1), with an absorption maximum at 290 nm (ε 1700). This decays by a second-order path (k_d 1.5 × 10⁹ M^?1 s^?1) at a rate ～ 100-fold faster than the decay of TcO₄^2? under similar conditions.     

Photoelectron spectroscopy of silicon and germanium-fluorine binary cluster anions (SinF m − , GenF m − )

Electronic properties of silicon-fluorine and germanium-fluorine cluster anions (Si_nF _m ^? n = 1–9, m = 1–3, Ge_nF _m ^? ; n =1–9, m = 1–3) were investigated by photoelectron spectroscopy using a magnetic-bottle type electron spectrometer. The binary cluster anions were generated by a laser vaporization of a silicon/germanium rod in an He carrier gas mixed with a small amount of SiF₄ or F₂ gas. Comparison between photoelectron spectra of Si_nF^?/Ge_nF^? and Sin /Gen (n = 4–9) gives the insight that the doped F atom can remove one electron from the corresponding Sin _n ^? /Ge _n ^? cluster without any serious rearrangement of Sin/Gen framework, because only the first peak of Si _n ^? /Ge _n ^? , corresponding singly occupied molecular orbital (SOMO), disappears and other successive spectral features are unchanged with the F atom doping     

Gas phase oxidative-addition reactions of alkyl radicals at complexed cobalt(II) centres

Negative chemical ionisation mass spectrometry is used as a probe to identify reactions between hydrocarbon radicals and cornplexed cobalt(II) centres in the gas phase. Methane NCI mass spectra of a series of cobalt(II) complexes containing O₄, O₂N₂ and N₄ donor atom sets are characterised by adduct ions of the form [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Formation of such ionic species has been rationalised in terms of a one-electron oxidative-addition mechanism involving attack by hydrocarbon plasma-derived alkyl radicals at the metal centre prior to electron capture: Co^IIL_n + R^? → RCo^IIIL_n$\text{e}{}^{\mathrm{?}}$ [Co^IL_n]^?. The competing resonance electron attachment reaction: Co^IIL_n$\text{e}{}^{\mathrm{?}}$ also occurs within the ion source.     

Quasi-resonant energy transfer in collisions: Na2(A1Σ u + )+K(4S)

Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na₂(A) to potassium atoms as described by Na₂(A¹Σ _u ⁺ ,v′J′)+K(4S)→Na₂ (X¹Σ _g ⁺ ,v″J″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimerv′J′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm^?1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm^?1) the cross section is Q=7.8×10^?13 cm².     

Analytical results for the classical and semiclassical coordinate probability distribution function of anharmonic oscillators

The classical and Wigner—Kirkwood semiclassical distribution functions for single and double-well anharmonic oscillators with ? = p?²/2m + k₂x?² + k_2nx?²ⁿ are given in closed form. Applications in the theory of electron diffraction are discussed briefly.     

Compared electronic structure of negative ions M p C n − : I. Normal elements in Hückel theory

Negative cluster ions M _p C _n ^? (M normal element,n<10,p=1?4) produced by various experimental techniques from carbides show in their emission intensities a very strong even-odd effect according to the parity of the carbon atom numbern. This is in particular the case when M=N, F, Cl (p=1), M=H, Al, Si, S (p=1, 2) or M=B (p=1?4). The largest intensities of M _p C _n ^? ions always take place for evenn except in the cases of NC _n ^? , B₂C _n ^? and Al₂C _n ^? , for which the maxima of emission occur for oddn. This oscillating behaviour corresponds to alternations in the stability of the clusters which are mainly due to the fact that, in Pitzer and Clementi model (linear chains in thesp hybridization within the framework of Hückel theory), the HOMO (highest occupied molecular orbital) of the clusters lies in a double degenerateπ level band: a cluster with a complete HOMO is always more stable than a cluster with a nearly empty HOMO. This result involves that the total number ofπ electrons is the main factor governing the parity of the stability alternations. Accordingly, since the knowledge of theπ electron number requires the determination of theσ electron number too, these alternations enable us to infer a very likely electronic structure of the ions.     

Residual photocurrent at a mercury electrode

The residual photocurrent observed at negative potentials with mercury in contact with slightly alkaline 1 M KCl solution has been reinvestigated and found to be caused partly by the reaction of e^?_aq with traces of unidentified electron acceptors and partly by reaction with the solvent. Such a solution can be freed from electron-accepting impurities by irradiation with light of shorter wavelength than 270 nm if SO^2?₃ is present at low concentration. The time constant for the homogeneous decay of e^?_aq at pH ca. 8.8 is then raised to about 400 μs. This slow decay is due to reaction with the solvent as the decay time constant can be increased considerably by raising the pH of the solution. In unsteady state experiments with purified 1 M KCl solutions of high pH containing no added scavenger for e^?_aq the current connected with electron emission and e^?_aq diffusion towards the electrode and the bulk of the solution, is cancelled out at ca. ?1.4 V vs. SCE by a thermal non-faradaic current component when 360 nm light is employed. When CO₂ is present at high concentration a similar cancellation is observed at lower pH at ca. ?1.1 V vs. SCE, suggesting a value for the diffusion coefficient of the radical-ion CO^?₂ about 3.3 times smaller than that of e^?_aq.