Mechanism of the oxidation reaction of Cu with N2O via nonadiabatic electron transfer

We treat the present work as an attempt to elucidate the mechanism of the oxidation reaction of the Cu atom by nitrous oxide based on our recent work (Kryachko, E. S.; Vinckier, C.; Nguyen, M. T. J Chem Phys 2001, 114, 7911) on the electron attachment to this molecule. We suggest that the title reaction in its Arrhenius regime occurs via the nonadiabatic electron transfer from Cu to the oxygen atom at the crossing of the potential energy surfaces Cu(4s ²S_1/2) + N₂O(X ¹Σ⁺) and Cu⁺ + N₂O^?, where the latter is linked to the complex N₂O^? originated from the higher‐energy T‐shape N₂O molecule and discovered in the aforementioned work. The calculations performed in the present work using a variety of quantum chemical methods support the proposed model. We also show the existence of other reaction pathways of the title reaction that, we believe, contribute to its non‐Arrhenius behavior observed experimentally at T > 1190 K. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Semiclassical description of multiple electron capture and ionization in fast bare nucleus-rare gas collisions

Multiple electron capture plus ionization processes inX ⁱ⁺-Ne collisions (i=6, 12, 20) in the energy regime from 50 keV/amu up to several MeV/amu are studied within a semiclassical quantum statistical (?=0) independent particle model. Good agreement is found with existing experimental data for the production of recoil ions with charges up toq=8.     

Vicinage effect in secondary electron emission from a clean (001) surface of SnTe induced by keV hydrogen clusters

The total secondary electron emission yields from a clean (001) surface of SnTe crystal are studied at the bombardment of hydrogen clusters (H⁺, H ₂ ⁺ and H ₃ ⁺ ions) with energies ranging from 7 to 12 keV/amu. The observed yield is not proportional to the number of protons in the cluster ion. The yields are successfully explained by applying the stopping powers of a homogeneous electron gas for the constituents of the clusters in keV energy region, which provide the vicinage effect.     

Resonance states of atomic anions

We study destabilization of an atom in its ground state with decrease of its nuclear charge. By analytic continuation from bound to resonance states, we obtain complex energies of unstable atomic anions with nuclear charge that is less than the minimum “critical” charge necessary to bind N electrons. We use an extrapolating scheme with a simple model potential for the electron, which is loosely bound outside the atomic core. Results for O^2? and S^2? are in good agreement with earlier estimates. Alternatively, we use the Hylleraas basis variational technique with three complex nonlinear parameters to find accurately the energy of two‐electron atoms as the nuclear charge decreases. Results are used to check the less accurate one‐electron model. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 255–261, 2001     

A quasielastic scattering approximation for target ionisation by heavy structured projectiles

A modification of the impulse approximation for capture to continuum is used to describe the ejection of loosely bound target electrons by heavy ions. In contrast to the currently applied elastic scattering models based on the binary encounter approximation, the present model treats only the short-range part of the ionic field within the elastic scattering theory, but uses the more sophisticated impulse approximation for the Coulomb tail of the interaction potential. Calculations have been performed for B ^q+, Fe ^q+, Au ^q+ and U ^q+ colliding with helium at energies between 0.5 and 6 MeV/amu. The comparison with absolute experimental spectra shows that theory works well for light projectiles, being able to describe the intensity and its variations with ionic chargeq _ion in the binary encounter peak region. For very heavy low-energy projectile ions the intensity is, however, seriously under-predicted at small emission angles, indicating a breakdown of perturbative treatments.     

Dissociative Photoionization of Heterocyclic Molecule-Morpholine under VUV Synchrotron Radiation

The radiation damage of biomolecules, in particular with aliphatic compound, has been extensively studied. Morpholine is a typical six-membered aliphatic heterocyclic compound. In the present work, photoionization and dissociation of the morpholine monomer and subsequent fragmentations have been investigated by synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. The vertical ionization energy of morpholine monomer is 8.37±0.05 eV, which agrees reasonably well with a theoretical value 8.41 eV of morpholine. Experimentally observed fragmentation of morpholine (m/z=87 amu) gives rise to m/z=86 amu, m/z=57 amu, and m/z=29 amu. Based on experimental and theoretical results, it is found that the m/z=86 amu is produced by losingH atom, the m/z=57 amu is formed by the elimination of CH₂O with a ring-opening process, the m/z=29 amu is generated by further dissociation of the fragment m/z=57 amu (C₃H₇N)⁺ by the elimination of C₂H₄. This finding would provide valuable insight into the photo-damage of aliphatic compounds, which may be related to living cells and other biological system.     

Scandium dipivaloyl methanate as a volatile precursor for thin film deposition

The coupling of a quadrupole mass spectrometer (QMS) via a heated capillary to a commercial thermogravimetric analyser is described. The amu and temperature ranges available were up to 1000 amu and 1500°C, respectively. The system was evaluated with test compounds, yielding gaseous species in the m/z range of 17-80, and then used for the study of thermal behaviour of scandium dipivaloyl methanate or Sc(thd)₃ which is discussed in detail. Sc(thd)₂ appears as the major Sc-containing species with m/z=411 in the gas phase at 200-300°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Theoretical study of silicon–sulfur clusters (SiS2)n− (n=1–6)

The possible geometrical structures and relative stability of silicon–sulfur clusters (SiS₂) (n=1–6) are explored by means of density functional theory (DFT) quantum chemical calculations. We also compare DFT with second‐order Møller–Plesset (MP2) and Hartree–Fock (HF) methods. The effects of polarization functions, diffuse functions, and electron correlation are included in MP2 and B3LYP quantum chemical calculations, and B3LYP is effective in larger cluster structure optimization, so we can conclude that the DFT approach is useful in establishing trends. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS₂)_n⁻ are analyzed by B3LYP. As a result, the regularity of the (SiS₂)_n⁻ cluster growing is obtained, and the calculation may predict the formation mechanism of the (SiS₂)_n⁻ cluster. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 280–290, 2001     

Theoretical insight into the magnetic circular dichroism of uranium N6,7-edge X-ray absorption

We use ligand-field density functional theory to determine the electronic structure and to model magnetic circular dichroism in the X-ray absorption spectroscopy (XAS) of uranium compounds. This study extends earlier work on tetravalent uranium ion, in which a model Hamiltonian was set up in order to study electronic structure with three nonequivalent 4f, 5f, and 6d electrons. In the earlier work, the model Hamiltonian took into consideration the interelectron repulsion, spin-orbit coupling interaction, and ligand-field splitting. Uranium N_6,7-edge XAS spectra were calculated on the basis of the 5f² → 4f¹³5f²6d¹ electron transition, showing spectral profiles that were mainly dominated by 4f electron spin-orbit coupling, as well as 6d ligand-field splitting. Fine structures were also observed due to the interelectronic repulsion between 4f-5f, 4f-6d, and 5f-6d electrons. Here, the theoretical study is extended to take into consideration the presence of an external magnetic field, incorporating into the model Hamiltonian for three-open-shell electron configuration a term for Zeeman interaction. Therefore, we are able to model spectra with a left-circularly and right-circularly polarized X-ray, demonstrating evidence of X-ray magnetic circular dichroism (XMCD) for a tetravalent U⁴⁺ ion in the molecular (U(η⁸-C₈H₈)₂) complex. The XMCD originates from a ground-state electronic structure with open-shell 5f electrons. Furthermore, the present calculation of uranium N_6,7-edge XAS and XMCD spectra also enables the ligand-field bonding analysis of the coordination compound.     

Phenomenology of EPR Trapped Electron Spectra Produced by Photoionization in Alkalines at 4.2°k and 77°k

Trapped electrons, e_c^?, are produced by photoionization of K₄Fc(CN)₆ in 10M NaOH/H₂O and 10M NaOD/D₂O glasses at 4.2°K. The linewidth, ΔH_ms, of e_c^? changes reversibly between these two temperatures in contrast to the observations for organic matrics. Three proposed mechanisms including dipole relaxation of pendent molecules surrounding the electron cavity, contraction-expansion model of cavity, and electron retrapping process are each discussed. It appears that no one physical model satisfactorily accounts for the present observations. The electron retrapping process, however, might be a better condidate for interpreting the experimental results in compatible with the optical absorption data.     

Measurement of the4He-D2 mass difference

A Penning ion trap spectrometer has been used to measure the modified cyclotron frequencies of trapped⁴He⁺ and D ₂ ⁺ ions. The resonances were detected by a time of flight method after ejection of the ions from the trap. We obtain a mass differenceΔm (D₂-⁴He) = 25600331(5)·10^?9 amu in acordance with published values but with a reduced uncertainty.     

A New Modified Pseudoequilibrium Calculation to Determine the Composition of Hydrogen and Nitrogen Plasmas at Atmospheric Pressure

This paper proposes a modified pseudoequilibrium calculation, which gives almost the same results as those of kinetic calculations to determine the composition of hydrogen and nitrogen plasmas at atmospheric pressure. The computing time is two to three orders of magnitude faster than that of the kinetic calculations. First, according to experimental results, a relationship between the electron temperature T_e and the heavy species one T_h has been proposed. The ratio T_e/T_h varies as a function of the logarithm of the ratio n_e/n _e ^max , _e ^max being the electron density in the plasma core for which equilibrium is achieved _e ^max ~ 10 ²³ ). The kinetic calculations have been performed assuming the microreversibility where the backward kinetic rate coefficient k_b is calculated by k_d/k_b=K_x, where k_d is the direct kinetic coefficient and K_x the molar fraction equilibrium constant. When electrons are involved in both direct and backward reactions, k_d and K_x are expressed as functions of T_e . However, when the direct reaction involves electrons while the backward one is due to collisions between heavy species (or the reverse), a temperature T* between T_e and T_h is introduced. T* is determined as a function of the ratio of the electron flux to that of neutral species in such a way that T*=T^e for n_e > 10²³ and T*=T_h for low values of n_e(n_e < 10¹⁵ m^–3). Compared to hydrogen, the nitrogen composition exhibits a very abrupt variation between 6000 and 6500 K, corresponding to a shift from the dissociation-dominated regime to that of ionization. It occurs because dissociation of nitrogen starts almost simultaneously with its ionization, which is not the case of H₂, for which dissociation is terminated long before ionization starts. If the charge transfer reaction, whose activation energy is low for both gases, is neglected, in both cases the electron density increases drastically below 9000 K. These results are quite similar to those obtained when calculating the composition with the multitemperature mass action law. The kinetic calculations are dominated by the reactions with a low activation energy: dissociation, dissociative recombination and charge transfer. Thus, a modified pseudoequilibrium calculation has been introduced, the plasma composition being calculated with the equilibrium constants corresponding to low activation energies[X₂ 2X, e+X ₂ ⁺ 2X, X ₂ ⁺ +X X⁺ + X₂ both for hydrogen (X=H) and nitrogen (X=N)] at the temperature T* between T_e and T_h. The results are in very good agreement with those of the kinetic calculations.     

The catalytic reduction of nitrobenzene at the [MoVIO2(O2CC(S)(C6H5)2)2]2− complex intercalated in a Zn(II)–Al(III) layered double hydroxide host: A kinetic model for the molybdenum–pterin binding site in nitrate reductase

The heterogeneous reduction of nitrobenzene by thiophenol catalyzed by the dianionic bis(2‐sulfanyl‐2,2‐diphenylethanoxycarbonyl) dioxomolybdate(VI) complex, [Mo^VIO₂(O₂CC(S)(C₆H₅)₂)₂]²⁻, intercalated into a Zn(II)–Al(III) layered double hydroxide host [Zn_3−xAl_x(OH)₆]^x+, has been investigated under anaerobic conditions. Aniline was found to be the only product formed through a reaction consuming six moles of thiophenol for each mol of aniline produced. The kinetics of the system have been analyzed in detail. In excess of thiophenol, all reactions follow first‐order kinetics (ln([PhNO₂]/[PhNO₂]₀) = −k_appt) with the apparent rate constant k_app being a complex function of both initial nitrobenzene and thiophenol concentrations, as well as linearly dependent on the amount of solid catalyst used. A mechanism for this catalytic reaction consistent with the kinetic experiments as well as the observed properties of the intercalated molybdenum complex has thiophenol inducing the initial coupled proton–electron transfer steps to form an intercalated Mo^IV species, which is oxidized back to the parent Mo^VI complex by nitrobenzene via a two‐electron oxygen atom transfer reaction that yields nitrosobenzene. This mechanism is widespread in enzymatic catalysis and in model chemical reactions. The intermediate nitrosobenzene thus formed is reduced directly by excess thiophenol to aniline. The values of rate coefficients indicate that reduction of nitrobenzene proceeds much faster than proton‐assisted oxidation of thiophenol. This may account for the observation that the presence of protonic amberlite IR‐120(H) increases considerably the rate of the overall reaction catalyzed. Activation parameters in excess of the protonic resin and PhSH were ΔH^≠ = 80 kJ mol⁻¹ and ΔS^≠ = −70 J mol⁻¹ K⁻¹. The large negative activation entropy is consistent with an associative transition state. The present system is characterized by a well‐defined catalytic cycle with multiple‐turnovers reductions of nitrobenzene to aniline without appreciable deactivation. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 212–224, 2001     

An atom-in-molecules and electron-localization-function study of the interaction between O2 and VxOy+/VxOy (x = 1, 2, y = 1–5) clusters

 The most stable structures of V _x O _y ⁺/V _x O _y (x=1, 2, y=1–5) clusters and their interaction with O₂ are determined by density functional calculations, the B3LYP functional with the 6-31G* basis set. The nature of the bonding of these clusters and the interaction with O₂ have been studied by topological analysis in the framework of both the atoms-in-molecules theory of Bader and the Becke–Edgecombe electron localization function. Bond critical points are localized by means of the analysis of the electron density gradient field, ∇ρ(r), and the electron localization function gradient field, ∇η(r). The values of the electron density properties, i.e., electron density, ρ(r), Laplacian of the electron density, ∇²ρ(r), and electron localization function, η(r), allow the nature of the bonds to be characterized, and linear correlation is found for the results obtained in both gradient fields. Vanadium-oxygen interactions are characterized as unshared-electron interactions, and linear correlation is observed between the electron density properties and the V–O bond length. In contrast, O₂ units involve typical shared-electron interactions, as for the dioxygen molecule. Four different vanadium–oxygen interactions are found and characterized: a molecular O₂ interaction, a peroxo O₂ ²⁻ interaction, a superoxo O₂ ⁻ interaction and a side-on O₂ ⁻ interaction. Received: 15 October 2001 / Accepted: 30 January 2002 / Published online: 24 June 2002     

Theoretical investigation of the cyclic GaO2 and GaS2 molecules at DFT and correlated wave function levels

The geometries and the bonding properties have been predicted for cyclic GaO₂ and GaS₂ species at density functional theory (DFT), MPn (n=2,3,4 with different substitutions), QCISD(T), and CCSD(T) all‐electron correlation levels with 6‐311+G* basis set. The geometrical optimizations and the harmonic vibrational frequency analysis are performed using DFT and second‐order Møller–Plesset (MP2) methods. The relevant energy quantities are also calibrated at the high‐order electron correlation levels [MP3, MP4, quadratic configuration interaction (QCI), and coupled cluster (CC)]. Each species possesses a ²A₂ ground state with a higher energy level ²A₁ state. The corresponding state–state separations are about 32 kcal/mol for GaO₂ species and about 20 kcal/mol for GaS₂ species at the QCISD(T)/6‐311+G* level. The QCISD(T) and CCSD(T) calculations yield dissociation energies of 42.0 and 59.0 kcal/mol for two species, respectively, and other methods yield dissociation energies within ∼5 kcal/mol. Result analysis has indicated that the cyclic GaO₂ should be classified as superoxide and the GaS₂ species should be classified as supersulfide in their ground state, and those in the excited state (²A₁) should not be. However, the cyclic GaS₂ (²A₂) is less ionic than the GaO₂ (²A₂) and they are far less ionic than NaO₂. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 222–231, 2001     

Dissociative Electron Attachment to Hexachlorobenzene

Gas phase molecules of hexachlorobenzene (C₆Cl₆) were investigated by means of dissociative electron attachment spectroscopy (DEAS). Three channels of molecular negative ions decay have been identified: abstraction of Cl⁻ and Cl₂⁻ as well as electron detachment (τ_a∼250 μs at 343 K). All three channels exhibit temperature dependence. The adiabatic electron affinity estimated using a simple but typically accurate Arrhenius model (EA_a=1.6–1.9 eV) turns out to be much higher than the quantum-chemical predictions (EA_a=0.9–1.0 eV). We discuss the possible reasons behind the observed discrepancy.     

A Novel Bicyclophosphite Ligand Directly Yields Rhodium Hydride Complexes

Summary.  Complexation of Rh(I) with o, o′-dimethylene-(tris-p-cresyl)-bicyclophosphite (BCP, 1) has been investigated in solution by NMR, semi-empirical quantum mechanical, and molecular mechanics calculations. ¹H and ³¹P NMR spectroscopic data show that when the BCP/Rh ratio exceeds 2, Rh hydride complexes of the composition RhH(BCP)₃ and RhH(BCP)₄ are formed. The source of the hydride ion is the ligand itself; most probably, H⁻ originates from the bridging CH₂ groups of BCP. The chemical shifts of these protons are sensitive to complexation due to the considerable electron density of HOMO and LUMO at one of the bridging CH₂ moieties. Molecular mechanics simulations of the molecular structure of these complexes show that two cavities are formed in [Rh(BCP)₃]⁺ by the aromatic rings of the ligands. These cavities may alternatively open and close, thus providing for a flexibly shielded catalytic site which explains the unusual catalytic behaviour of Rh complexes with BCP in hydrogenation and hydroformylation reactions. Received February 15, 2001. Accepted (revised) April 23, 2001     

Synthesis and properties of σ–π conjugated alternating polymers consisting of carbazole and organosilicon units

We have synthesized novel σ–π conjugated polymers with an alternating organosilanylene and π‐electron system, intending to utilize them for hole‐transporting materials of electroluminescent (EL) devices. 3,6‐Di(lithioethynyl)carbazoles were co‐polymerized with organodichlorosilanes to give the corresponding polymers with molecular weights of M_W = 2000–5000. Another type of polymer with a thienylene unit was also synthesized by the nickel‐catalyzed reaction of the di‐Grignard reagent of 1,2‐bis[2‐(5‐bromothienyl)]tetraethyldisilane with 3,6‐dibromocarbazole, the molecular weight being M_n = 3100. The EL devices with a double‐layer system composed of tris(8‐quinolinolato)aluminum(III) and the present polymers as the emitting‐electron‐transporting and hole‐transporting layers, respectively, emit green EL with a maximum intensity of the order of 10³ cd m^?2. Of these, the device with the thienylene–carbazole polymers exhibited the highest luminance of 1480 cd m^?2. Copyright © 2001 John Wiley & Sons, Ltd.     

Pseudorotational dynamics of H3+ and Li3+

The origin of the pseudoprecession phenomenon is investigated through a computational study of the time evolution of H₃⁺ and Li₃⁺ by electron nuclear dynamics theory. In particular, the pseudorotation of both molecules is shown to induce a spatial rotation, which in turn leads to Coriolis coupling of the two orthogonal nuclear shape deformation modes. This effect is rooted in an anisotropy of the molecular ground state potential energy surface that is caused by the interaction between the D_3h ground state and a twofold degenerate first excited state. Computations are performed for a variety of vibrational energies. In addition, the impact of the anharmonicity of the ground state potential surface on the shape deformation modes and the coupling between them is discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001