Effect of the group IV elements on the Π anion and cation states of thiophene and furan determined by means of ETS and UPS

The electron-transmission and He(I) photoelectron spectra of Si(CH₃)₃, Sn(CH₃)₃ and CH₂Si(CH₃)₃ derivatives of thiophene and furan have been recorded. The first two substituents perturb the energies of the outer filled π orbitals and of the empty π* orbitals in opposite directions, causing a reduction of the HOMO/LUMO energy separation. The stabilization experienced by the π* MO's depends on their wavefunction coefficients at the site of substitution, and is attributed to interaction with low-lying empty orbitals of the substituent groups. The relatively small size (～ 0.4 eV) of this effect on the unoccupied ring MO's suggests that it should not appreciably affect the energy of the filled MO's.The strong conjugation between the π* unoccupied orbital of the nitro group and those of thiophene has also been investigated.     

Spectre de photoélectrons He(I) De l'hexafluorobicyclo[2,2,0]-hexadiéne-2,5

The He(I) photoelectron spectrum of C₆F₆ (hexafluorobicyclo[2.2.0]hexa-2,5-diene) has been recorded. The ionization energy of the compound is measured to be 10.08 eV. The energy difference, 0.87 eV, between the two first bands of the PE spectrum is attributed to homoconjugation (through-space interaction) between the two double bonds. The highest occupied MO is shown to be of b₂ symmetry (C_2v group), the next one being of a₁ symmetry.EXTHUC, CNDO and INDO methods have been used to calculate the changes of the total energy of the molecule and of the two highest occupied MO's upon variation of the dihedral angle of the molecule.     

Relative partial photoionization cross-sections and photoelectron branching ratios of ethylene

Relative partial photoionization cross-sections and photoelectron branching ratios of the valence bands (~10–25 eV binding energy) of ethylene are reported over the photon energy ranges 18–100 eV and 21–100 eV, respectively. The four lowest ionization energy bands (1b⁻¹_1u, 1b⁻¹_1g, 3a⁻¹_g, and 1b⁻¹_2u) show monotonic cross-section decreases with photon energy from 33 eV, the 1b⁻¹_1u CC π band showing the least rapid decline. In contrast, the 2b⁻¹_3u and 2a⁻¹_g bands show almost constant cross-sections up to ~50 eV photon energy, followed by similar, although slower, monotonic decreases. This is attributed to the substantial carbon 2s character of the 2b_3u and 2a_g orbitais. The cross-section behaviour of all bands is interpreted with the aid of SCF-LCAO-MO calculations on the neutral molecule using the Gaussian-80 series of programs.     

Synthesis and redox behavior of a new polyanion compound, Li2Co2(MoO4)3, as 4 V class positive electrode material for lithium batteries

A new material, Li₂Co₂(MoO₄)₃, belonging to NASICON type polyanion family was synthesized by means of a low temperature soft-combustion method using glycine as a soft combustion fuel. The annealed product, Li₂Co₂(MoO₄)₃, was found to exhibit a single phase structure as confirmed by XRD and crystallized in an orthorhombic structure (space group Pnma) with lattice parametersa=5.086(1) Å,b=10.484(2) Å and c=17.606(2) Å. The electronic state of each element present in the new material was confirmed by X-ray photoelectron spectroscopic (XPS) analysis. The stoichiometry of the synthesized product was determined by the metal analysis using inductively coupled plasma (ICP-AES) technique. The microstructural analysis by means of SEM revealed cylindrical fiber-like grains. Electrochemistry of the new material was demonstrated by extraction/insertion process of Li⁺ in lithium batteries. Galvanostatic charge/discharge profiles revealed a reversible discharge capacity of ～ 55 mAh/g over the potential window of 4.9 - 1.5 V.     

Announcement

The He(I) and He(II) photoelectron spectra of benzoyl chloride have been subjected to a relative band intensity analysis. The spectral assignment, which is supported by theoretical ionization cross-sections calculated from a GAUSSIAN 70 wavefunction, illustrates the use of He(II) radiation for molecules containing heavy atoms. The low ionization potentials of benzoyl chloride are described in molecular orbital terms as π < π < n_o < n_C? ～ ⁿ_Cl.     

A pes study on 1,3-thiazole and its monosubstituted halogen derivatives

The photoelectron (HeI) spectra of 1,3-thiazole and its 2F, 2Cl, 2Br, 4Br and 5Br-derivatives are reported. The assignment of the first few bands of the various spectra to the corresponding molecular orbital is based, for thiazole, on the results of an ab initio SCF—MO calculation, while for the various halogen derivatives, on reasonings based on perturbation theory.In particular, the first five outermost molecular orbitals of thiazole probably correspond to π₃ (9.50 eV), π₂ (10.24), σ_N (10.48; orbital mainly localized on the nitrogen atom), σ_S (12.78; orbital mainly localized on the sulphur atom) and π₁ (13.5).     

Photoelectron (He(I), He(II) and X-ray) spectroscopy of γ-pyrone and its related sulphur derivatives: valence and core ionization energies and shake-up satellites

The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one (1), 4H-thiopyran-4-one (2), 4H-pyran-4-thione (3) and 4H-thiopyran-4-thione (4) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are n_X (σ), 3b₁ (π), 1a₂(π) for 1, 2 and 4; and 3b₁(π), n_X(σ) and 1a₂(π) for 3. The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3b₁ (π) → 4b₁(π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom.     

Influence of one CO molecule on structural and electronic properties of monatomic Cu chain

By using first-principles calculations, we have systematically investigated the structural and electronic properties of an infinite linear monatomic Cu chain with an adsorbed CO molecule. We find that the bridge geometry is energeticabsally favored not only when the Cu–Cu bond below the molecule is unstretched, but also for a wide range of d_Cu–Cu up to about 4.20 Å, while the substitutional geometry is favored only in the hyperstretched situation d_Cu–Cu>4.80 Å. Charge density differences point out the electron transfer is from the Cu atoms to the adsorbed CO molecule. The binding mechanism of CO to Cu chain can be described by the Blyholder’s model, in terms of σ-donation of electron density from the nonbonding CO-5σ orbital into empty metal orbitals and π-backdonation from the occupied metal d orbitals to empty CO-2π^⁎ orbital. The donation/backdonation process leads to the formation of bonding/antibonding pairs, 5σ_b/5σ_a and 2π_b^⁎/2π_a^⁎, with the 5σ_a lying above E_f and the 2π_b^⁎ below E_f.     

(e,2e) Spectroscopy of ethane

The 400-eV and 1200-eV non-coplanar symmetric (e, 2e) reaction has been used to measure the momentum distributions of electrons in the individual valence orbitals of ethane as well as to measure the complete separation energy spectra in the valence region. The shapes and relative magnitudes of the momentum distributions agree well with those calculated using the plane wave off-shell impulse approximation and double zeta basis molecular orbital wave functions. The ground state of C₂H₆⁺ is shown to be 1e_g^?1, with the vertical ionization potential being 12.25 ± 0.1 eV. Considerable structure due to configuration interaction is observed in the separation energy region 29–55 eV. Much of this structure can be assigned to the 2a_1g orbital.     

A new crystalline form of carbon based on the C36 fullerene: Simulating its crystal and electronic structure

A new crystalline allotropic form of carbon consisting of covalently bound fullerenes C₃₆ of symmetry D _6h is suggested. The structure of the unit cell of this compound was simulated. The unit-cell parameters obtained (a=b=6.695 Å and c=6.763 Å) are close to experimental data. The band structure of the spectrum of valence electrons was calculated by the method of crystal orbitals. The bandgap was found to be ～1.9 eV. The energy-band structure of quasi-one-dimensional macromolecules [C₃₆]_n(n?1) is discussed depending on the way in which the monomers are bound in them.     

The photoelectron and absorption spectra of allyl halides

The ultraviolet photoelectron spectra (5–20 eV) absorption spectra (1400–2500 Å) of allyl C₃H₅X (X = F, Cl, Br, I) have been measured. The ionisation potentials between 5–16 eV are determined and the type of orbital is interpreted with the aid of the vibration pattern and the band form.From these spectra several conclusions can be drawn concerning the iodide: (1) the ionisation potential of the π_C_C system of allyl iodide is lower than expected when compared to the ionisation potential of the corresponding band of the other halides. (2) The splitting of its np lone pair photoelectron bands is not in accordance with the expected splitting associated with spin-orbit coupling. (3) One of the two components of the lone pair bands has been broadened. These observations can be explained by a through-space interaction of one of the iodine “lone pairs” with the π-system.     

Water adsorption on the Be(0001) surface: from monomer to trimer adsorption

In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be(0001) surface. In our calculations, the adsorbed water molecules are energetically favoured adsorbed on the atop sites, and the dimer adsorption is found to be the most stable with a peak adsorption energy of ～437 meV. Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3a₁-like molecular orbital with the (s, p_z) orbitals of the surface beryllium atoms. While in the case of the water dimer adsorption, the 1b₁-like orbital of the H₂O molecule plays a dominant role.     

Ab initio calculation of the first ionization potential in linear alkanes using exciton theory

An ab initio calculation is used to give the form of the ionization potential in the alkane series and to explain the origin of the various contributions to this potential. The question of whether the ionization relates to a σ-type orbital, composed mainly of carbon atomic orbitals, or to a π-type, composed of CH bonds, is considered. The results show a gradual evolution from a CH ionization (13·26 eV) in CH₄ to a CC ionization (10·0 eV) at the farthest limit of the series.     

The photoelectron spectra of cyclooctatetraene and its hydrogenated derivatives

The photoelectron spectrum of cyclooctatetraene (COT; 1) has been re-examined. Correlation with the spectra of the dihydro- (2, 3), tetrahydro- (4, 5, 6), hexahydro- (7) and octahydro- (8) derivatives confirms the orbital sequence originally proposed by Eland, namely 5a₁ (π), 7e (π), 4b₂ (π), σ. It is shown that the positions and the relative spacing of the π-orbitals are the result of a competition between through-space and through-bond interactions.The photoelectron spectroscopic results for the hydrogenated derivatives of COT yield information about their conformation; in particular about the twist angles between consecutive π-bonds. The spectrum of 1,5-cyclooctadiene (6) confirms that this molecule preferentially adopts the boat conformation.An empirical rule is proposed which yields estimates for the orbital energies of basis π-orbitals in monocyclic hydrocarbons.     

Extended Huckel calculations on the Pi system of polyaniline

The pi molecular orbitals of aniline are used in a tight-binding calculation, within the extended Huckel methodology, to find the energy band structure of head-to-tall polyaniline. The highest occupied band, the 3b₁, is also the widest band with width=1.7eV. This band can be depopulated either by oxidation or protonation to give a metal-like conductive state. Alternately, oxidation can lead to quinoid-like defect sites along the polymer chain that give midgap states that could be responsible for conductivity. The lowest unoccupied state is the localized 2a₂ orbital positioned 3.0eV above the top of the 3b₁ band. Because of the localized nature of this state, reductive doping should not be an effective method for improving the conductivity of polyaniline.     

Structural changes during the unfolding of Bovine serum albumin in the presence of urea: A small-angle neutron scattering study

The native form of serum albumin is the most important soluble protein in the body plasma. In order to investigate the structural changes of Bovine serum albumin (BSA) during its unfolding in the presence of urea, a small-angle neutron scattering (SANS) study was performed. The scattering curves of dilute solutions of BSA with different concentrations of urea in D₂O at pH 7.2 ± 0.2 were measured at room temperature. The scattering profile was fitted to a prolate ellipsoidal shape (a, b, b) of the protein witha = 52.2 Å andb = 24.2 Å. The change in the dimensions of the protein as it unfolds was found to be anisotropic. The radius of gyration of the compact form of the protein in solution decreased as the urea concentration was increased.     

Investigation of the metastable state of Na2[Fe(CN)5NO] · 2H2O by optical spectroscopy. II The electronic spectra of the ground and metastable states

The absorption spectra of Na₂[Fe(CN)₅NO] · 2H₂O were measured in the visible region in the range of 3400–7000 Å. In the metastable state, an additional absorption band in the long wavelength range is observed and the transition $\text{2}\text{b}{}_{\mathrm{<mtext>2</mtext>}}\text{(d}{}_{\mathrm{xy}}\text{)→}\text{7}\text{e(π}{}^1\text{?NO}\text{)}$ becomes weaker in the excited state indicating a population of the π¹(NO)-orbital. The laser excited emission spectrum shows a broad luminescence beginning at the excitation line $\text{λ =}\text{5145}\text{A}\text{?}\text{(}\text{19,436 cm}{}^{-1}\text{)}$ with a maximum at about 6250 Å (16,000 cm^-1). A strong sharp luminescence at about 7836 Å is registered and may be assigned to a transition 3b₁(d_x²?y²) or 5a₁(d_z²) to the antibonding π¹(NO)- orbital. Further the broad luminescence is superimposed by a series of sharp spikes. These sharp spikes can also be observed for several days, when the laser is switched off, and are depending on the crystal orientation.     

Relaxed energy and structure of edge dislocation in iron

With modified analytical embedded-atom method and molecular dynamics simulation, this paper simulates the strain energy and the equilibrium core structure of a<100> edge dislocation in BCC metal iron on atomistic scale. In addition, the trapping effect of dislocation on vacancy is investigated as well. The results show that the equilibrium dislocation core is quite narrow and has a C_2v symmetry structure. Calculated strain energy E_s of the dislocation is a linear function of ln (R/2b) while R≥5.16 Å (1 Å=0.1 nm), in excellent agreement with the elasticity theory prediction. Determined core radius and energy are 5.16 Å and 0.62 eV/Å, respectively. The closer the vacancy to the dislocation line is, the lower the vacancy formation energy is, this fact implies that the dislocation has a trend to trap the vacancy, especially for a separation distance of the vacancy from dislocation line being less than two lattice constants.     

Angle-resolved photoelectron spectra of ethylene as a function of photon energy using synchrotron radiation

As a test of the applicability of multiple-scattering theory to an unsaturated organic system, angle-resolved photoelectron spectra of the first four bands of ethylene have been measured from 1.5 eV above threshold to a photon energy of 28 eV. The results are compared to the multiple-scattering theory calculations of Grimm. The comparisons are excellent except for the 1 b_3u orbital below 14 eV, and the disagreement is attributed to the occurrence of autoionization. It is found that the π orbital has a much higher β value than the σ orbitals, but the β value for the π orbital varies more rapidly than that for the σ orbitals from threshold to ～0.5 Rydberg (～7 eV).