C 1s NEXAFS study of rare-earth’s (La,Eu)-graphite intercalation compounds

Electronic structure of unoccupied states of Eu- and thin surface layer of La-intercalation compounds was studied by light polarization dependent NEXAFS at the C 1s threshold in a bulk sensitive (E_kin=1–2 eV) and a more surface sensitive (E_kin=265 eV) partial electron yield mode. It was shown that the C 1s spectra in both cases are mainly characterized by the π*- and σ*-symmetry graphite-derived features. For both systems the π*-derived peak was found at similar energies of exciting photons as for pristine graphite. A decrease of relative intensity of the π*-originated structure in intercalation compounds can be understood by partial occupation of the π*-derived states upon intercalation due to a charge transfer from rare-earth (RE) atoms. NEXAFS features found on both sides of the π* response may be related to pd hybrids forming as a result of chemical interaction between RE atoms and graphite layers.     

Scattering of CO and N(2) molecules by a graphite surface

Measurements of angular distributions for the scattering of well-defined incident beams of CO and N(2) molecules from a graphite surface are presented. The measurements were carried out over a range of graphite surface temperatures from 150 to 400?K and a range of incident translational energies from 275 to over 600?meV. The behavior of the widths, positions and relative intensities of the angular distributions for both CO and N(2) were found to be quite similar. The experimental measurements are discussed in comparison with calculations using a classical mechanical model that describes single collisions with a surface. Based on the behavior of the angular distributions as functions of temperature and incident translational energy, and the agreement between measured data and calculations of the single-collision model, it is concluded that the scattering process is predominantly a single collision with a collective surface for which the effective mass is significantly larger than that of a single carbon atom. This conclusion is consistent with that of earlier experiments for molecular beams of O(2) molecules and Xe atoms scattering from graphite. Further calculations are carried out with the theoretical molecular scattering model in order to predict translational and rotational energy transfers to and from the molecule during scattering events under similar initial conditions.     

Elastic π± + 3He scattering

Differential cross sections have been measured at θ≈20–120° at 50, 100 and 200 MeV. Salient features of the angular distributions are Coulomb interference effects at 50 MeV and clear spin-flip contributions to π^? compared to π⁺ scattering in the angular region of θ≈80° dominated by the πN p-wave minimum. Comparison with optical model calculations account for the data up to 200 MeV while this first-order scattering theory misses conspicuous features of data at 295 MeV.     

Structure and electronic absorption spectra of isotruxene dyes for dye-sensitized solar cells: Investigation by the DFT, TDDFT, and QTAIM methods

The electronic structure of two photosensitizing isotruxene dyes used in Grätzel photoelectro-chemical cells has been investigated by the quantum-chemical methods of the density functional theory (DFT) and Bader’s topological analysis of the electron density. It has been shown that intramolecular interactions in the dye molecules stabilize the planar relative arrangement of isotruxene and cyano-acrylic structural fragments, which provides π-conjugation over the whole molecular backbone. Based on the time-dependent density functional theory (TDDFT) calculations and analysis of the Kohn-Sham orbitals, it has been found that the first vertical electronic transition in the spectra of the isotruxene dyes is a combination of a poorly resolved lπ*-type excitation and a well-resolved π-π* excitation. The π-π* excitation admixture is associated with the asymmetric structure of the isotruxene fragment and contributes significantly to the intensity of the first electronic transition.     

Semi-empirical calculations of the zero-field-splitting parameters of the lowest triplet states of aromatic ketones

Semi-empirical calculations of zero-field-splitting parameters have been performed for the lowest triplet states of aromatic ketones, the mixing between the nearly degenerate n, π* and π, π* triplet states through the vibronic and spin-orbit interactions being considered. The results show that the mixing through the spin-orbit interaction is important to explain the absolute values and signs of the zero-field-splitting parameters observed for acetophenone, p-chlorobenzaldehyde, and benzophenone. The observed and calculated D values are -0·1943 cm^-1 and -0·180 cm^-1 for the lowest triplet state of p-chlorobenzalhyde in p-dibromobenzene.     

Manifestation of auger processes in C1s-satellite spectra of single-walled carbon nanotubes

Using the equipment of the Russian-German beamline of the synchrotron radiation at the BESSY II electron storage ring, satellite spectra accompanying the C1s core lines in the cases of single-walled carbon nanotubes and highly ordered pyrolytic graphite have been measured with a high energy resolution. The Auger spectra corresponding to shaking of the valence system of carbon by the core vacancy have been found and investigated. The Auger spectra of the studied single-walled carbon nanotubes and highly ordered pyrolytic graphite are caused by annihilation of the excited π* electron with a hole in the π subband. It has been established that the electron states in the conduction band have 3π* (gT, K, M) symmetry; i.e., they correspond to flat 3π* subband, which is localized by 12–13 eV above the Fermi level. It has been revealed that the general regularities of the distribution of electron states in the valence system insignificantly change during its shake-up by the excited core.     

Utilizing Experiment and Theory to Evaluate Rhodamine B ethylenediamine as a Fluorescent Sensor for G-type Nerve Agents

Nerve gas mimic binding with Rhodamine B ethylenediamine (1) was studied in organic media. Binding of the nerve gas mimic, diethyl chlorophosphate (DCP), with the probe generated a non-fluorescent intermediate and a fluorescent product. Fluorescent and non-fluorescent products generated were identified using mass spectrometry and X-ray crystallography. Time-dependent density functional theory calculations were also used to investigate the electronic structure of the fluorescent probe in the ground and lowest lying π?→?π* singlet excited state. Though good agreement between theory and experiment can be obtained for the intense peak in the experimental spectrum using non-hybrid functionals, care must be taken when modelling these complexes due to the appearance of an n?→?π* transition that is too low in energy and appears to fall in the shoulders of the π?→?π* transitions.

     

Direct graphene growth on Co3O4(111) by molecular beam epitaxy

Direct growth of graphene on Co(3)O(4)(111) at 1000 K was achieved by molecular beam epitaxy from a graphite source. Auger spectroscopy shows a characteristic sp(2) carbon lineshape, at average carbon coverages from 0.4 to 3 ML. Low energy electron diffraction (LEED) indicates (111) ordering of the sp(2) carbon film with a lattice constant of 2.5(±0.1) ? characteristic of graphene. Sixfold symmetry of the graphene diffraction spots is observed at 0.4, 1 and 3 ML. The LEED data also indicate an average domain size of ~1800 ?, and show an incommensurate interface with the Co(3)O(4)(111) substrate, where the latter exhibits a lattice constant of 2.8(±0.1) ?. Core level photoemission shows a characteristically asymmetric C(1s) feature, with the expected π to π* satellite feature, but with a binding energy for the 3 ML film of 284.9(±0.1) eV, indicative of substantial graphene-to-oxide charge transfer. Spectroscopic ellipsometry data demonstrate broad similarity with graphene samples physically transferred to SiO(2) or grown on SiC substrates, but with the π to π* absorption blue-shifted, consistent with charge transfer to the substrate. The ability to grow graphene directly on magnetically and electrically polarizable substrates opens new opportunities for industrial scale development of charge- and spin-based devices.     

用角动量投影壳模型研究129La的单准质子带

将角动量投影壳模型应用到¹²⁹La核,对单准质子带理论计算与实验结果进行了比较,与组态为πh_11/2的yrast带和组态为πg_7/2带的拟合令人满意-还确认了一个组态为πg_7/2［νh_11/2］²的扁椭球带- 关键词：     

Some aspects of shake-up phenomena in some simple polymer systems

Satellite peaks accompanying core ionizations are observed in polymers containing aromatic pendant groups. These satellites are absent in analogous saturated systems. CNDO/2 SCF MO calculations have been performed on model systems and the satellite peaks are interpreted as arising from shake-up processes involving π* ← π transitions in the aromatic system. The calculations correctly predict trends in satellite peak intensities and separations.     

Phenylacetylene chemisorbed on Pt (111), reactivity and molecular orientation as probed by NEXAFS Comparison with condensed multilayer and polyphenylacetylene

Near-edge X-ray absorption spectroscopy (NEXAFS) has been used to investigate the reactivity of phenylacetylene (PA) towards a Pt(111) surface and its molecular orientation. Spectra have been taken in the photon energy region 280–320 eV at both grazing and normal X-ray beam incidence angles with respect to the sample surface. NEXAFS K-edge spectra have been recorded for PA adsorbed in the monolayer as well as in the multilayer regime and, for comparison, the spectrum of the PA related polymer, polyphenylacetylene (PPA), has also been measured. The assignment of the π* and σ* resonances has been made on the basis of the chemical structure and interpreted with the help of ab initio calculations. Both the ionisation potentials for the C 1s electrons and the theoretical C K-edge absorption spectra have been calculated for all the six inequivalent carbon atoms of PA and of phenylethylene (PE) which is a model molecule for PPA. From the analysis of the data we have indication for an interaction involving mainly the CC triple bond of the acetylenic functional group of PA that undergoes opening and leads to the formation of a di-sigma bond with Pt, while the benzene CC bonds seem not affected. A polarization dependence has been evidenced for the π* resonances of PA adsorbed in monolayer condition indicating a molecular orientation of the phenyl ring π* orbitals between 37° and 34° relative to the normal to the crystal surface.     

Signatures of different carbon bonds in graphene oxide from soft x‐ray reflectometry

In graphene oxide, the graphite lattice is intercalated with oxygen groups that bond to carbon atoms. These groups have a bearing on the possibility of using graphene oxide as a precursor to make graphene. The nature of carbon bonds in graphene oxide has been characterized with soft x‐ray reflection spectroscopy across the carbon K‐edge. Results distinguish graphene oxide synthesized with Hummers' method from that made using a method suggested by Tour. The observed spectra are consistent with those from near‐edge x‐ray absorption fine structure (NEXAFS) measurements. In particular, the expected carbon K‐edge resonances associated with excitations into molecular π*‐ and σ*‐states of C? C bonds can be identified. Importantly, the greater oxidation efficiency of the method by Tour may be the reason for the observation of additional resonances that have been assigned to carbon bonding with molecular groups containing oxygen. The additional resonances have been interpreted as the excitations of carbon 1 s electrons into the carbonyl π*(C?O) orbital in the molecular group –COOH and into the hydroxyl π*(C? OH) orbital, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Rb晕带signature反转的机理

将角动量投影壳模型应用到84Rb核，对组态为πg9/2νg9/2的正宇称晕带和组态为π(p3/2,f5/2)νg9/2的负宇称晕带理论计算和实验结果进行了比较，特别是对正宇称晕带中的signature反转机理进行了探讨.角动量投影壳模型计算显示正宇称晕带中的signature反转是原子核随自旋增加形状发生变化的信号，其间原子核从低自旋的长椭球通过三轴形变变到高自旋的扁椭球.此外，还确定了此两带的原子核形状.     

Electronic properties of fluorenone in the excited states

The electronic spectrum of fluorenone has been studied by means of “molecules in molecules” calculations. Five π-π* transitions can be definitively assigned in the near-ultraviolet region. The electronic properties of the first singlet excited state obtained from solvent effects on the absorption and fluorescence bands are compared with the theoretical results.     

Ab initio SCF CI study of the electronic spectrum of s-tetrazine

Configuration interaction (CI) studies of ground, n→ π* and π→ π* electronically excited states are reported for s-tetrazine. The first n→ π* singlet excited state (¹ B _3u ), which is responsible for the purple-red colour of the molecule, is calculated at 2·80 eV, compared to the experimental transition energy of 2·22–2·70 eV. The singlet-triplet split of the first n→ π* states (¹ B _3u and ³ B _3u states) is calculated to be 0·76 eV.

The interaction of nitrogen lone pair orbitals (n-orbitals) is studied in terms of the ordering of the n π* excited states and found that the SCF orbital ordering is qualitatively in accord with the ordering of the n π* excited states in the CI level.

The first π→ π* excited state (¹ B _2u ) is calculated at 5·99 eV, slightly above the observed range of absorption. Numerous other high-lying singlet states as well as the triplet states have been calculated and they are used to verify several proposals relating to the excited state dynamics in the photo-physical studies of s-tetrazine.     

Anisotropy of the ultrasonic attenuation in soft tissues: measurements in vitro

This study was designed to measure the ultrasonic attenuation within phantoms and tissue samples over a broad bandwidth and at many angles of incidence with respect to intrinsic orientations in order to elucidate both the frequency and angular dependence of the attenuation coefficient. Significant angular dependence, or anisotropy, of the attenuation was observed in canine myocardium (maximum to minimum ratio: 2.2 to 1) and a tissue mimicking phantom of oriented graphite fibers in gelatin (max to min: 2 to 1). In control studies, insignificant anisotropy was observed in the attenuation in canine liver samples and phantoms with graphite powder suspended in gelatin. Comparisons of the magnitude of variations of the oriented-fiber phantom to that predicted by a viscous relative motion model are presented.     

Single spin asymmetries in charged pion production from semi-inclusive deep inelastic scattering on a transversely polarized 3He Target at Q2 = 1.4-2.7 GeV2

We report the first measurement of target single spin asymmetries in the semi-inclusive (3)He(e,e'π(±))X reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.16 < x < 0.35 with 1.4 < Q(2) < 2.7 GeV(2). The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The π(±) Collins moments for (3)He are consistent with zero, except for the π(+) moment at x = 0.35, which deviates from zero by 2.3σ. While the π(-) Sivers moments are consistent with zero, the π(+) Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and measured cross section ratios of proton to (3)He, and are largely consistent with the predictions of phenomenological fits and quark model calculations.     

Electron-energy bands in single-crystalline La-intercalated graphite

A graphite-intercalation compound (GIC) of La was prepared by a thermally induced surface reaction of a metallic La film on a graphite (0001) substrate. The LEED pattern shows a characteristic (√3 × √3) R30° reconstruction pointing to the formation of LaC₆. Angleresolved photoemission combined with Fermi-surfaces mapping reveals a strongly anisotropic electronic bandstructure of La-GIC. The unfolded π-symmetry graphitederived bands in the La intercalation compound may be described in good approximation within a simple rigidband model by charge transfer from La to graphite. Despite the presence of filled La-5d states large photoemission intensities close to the Fermi level around the K-points of the nonreconstructed Brillouin zone are related to carbon-derived p_π*-bands, which become partly occupied in the GIC.     

压力变化对再结晶石墨的影响

 用电子显微镜观察了不同压力下催化剂合金中花瓣状、类球状、片状再结晶石墨含量，晶粒形貌随压力变化的情况。得到如下结论：在高温高压条件下，利用过渡族金属合金作催化剂，在石墨向金刚石转化过程中，类球状再结晶石墨的存在是不可缺少的环节。     

Adsorption of CO on PtBi2 and PtBi surfaces

Approximate molecular orbital calculations have been applied to explain the low CO poisoning effects observed at PtBi₂ and PtBi electrodes. The bonding patterns for chemisorption of CO on the surfaces of Pt-Bi bulk alloys and pure Pt surfaces are quite similar. The major difference is not induced through much Pt-Bi bonding, but indirectly, by raising the Fermi level of the system, so that the C-O π* levels become practically filled upon interaction. This results in much lower adsorption energies than in the metallic Pt case, in accordance with experimental data. The calculations also imply C-O bond dissociation on the surface, a phenomenon not supported by experiment. CO adsorption at Pt-Pt bridge site (possible only on PtBi) is favored relative to atop chemisorption.