ESCA study of electronic structure of SmB6

The electronic structure of SmB₆ was investigated by X-ray photoelectron spectroscopy (XPS or ESCA). The spectrum of each core level of Sm in SmB₆ consists of three peaks. Such a splitting was not observed in Sm₂O₃, SmF₃, and SmB₄. The analysis of the results shows that three kinds of Sm ions — Sm²⁺(4f⁶), Sm²⁺(4f⁵5d^0.86s^0.2), and another Sm²⁺ — are present in SmB₆. The last kind of Sm ions is probably localized in a surface region.     

Rb掺杂C60单晶的相衍变和电子态

在C₆₀单晶超高真空解理面上制备C₆₀的Rb填隙化合物薄膜.用同步辐射光电子能谱研究了相衍变过程.观察到对应于固溶相、Rb₁C₆₀和Rb₃C₆₀的电子态密度分布.当数纳米厚Rb₃C₆₀薄膜在C₆₀单晶（111）解理面形成后，室温条件下进一步沉积Rb至样品表面不产生fcc到bct或bcc结构相变.C_{60 关键词： 4}C₆₀和Rb₅C₆₀吸附相')" href="#">金属性Rb₄C₆₀和Rb₅C₆₀吸附相 60单晶')" href="#">C₆₀单晶 相衍变 同步辐射光电子能谱     

Structural and electronic behavior of Sr2GdRuO6 complex perovskite

We report experimental and theoretical study of crystallographic lattice and electronic structure of Sr₂GdRuO₆ complex perovskite, which is used as precursor in the fabrication process of superconducting ruthenocuprate RuSr₂GdCu₂O₈. Samples were produced by the standard solid state reaction. Rietveld refinement of experimental X-ray diffraction patterns shows that material crystallizes in a monoclinic structure, which belongs to the P2₁/n (#14) space group, with lattice parameters , , , and tilt angle β=90.258. Calculations of electronic structure were performed by the density functional theory. The exchange and correlation potentials were included through the LDA+U approximation. Density of states (DOS) study was carried out considering the two spin polarizations. Results show Gd are majority responsible for the magnetic character in this material, but Ru contribution is also relevant because d-orbital is closer to Fermi level. Theoretical results evidence that Sr₂GdRuO₆ material behaves as a magnetic semiconductor, with 20μ_B effective magnetic moment.     

The electronic structure of Ca-intercalated superconducting graphite CaC6

We have measured Ca-intercalated graphite superconductor CaC₆ (T_c = 11.2 K) by soft X-ray photoemission spectroscopy in order to understand the electronic structure. For the valence band, we observed several structures that correspond to those of calculated density of states with the partial density of states of Ca 3d at the Fermi level (E_F). We also observed core level spectra that are a very large asymmetric Ca 2p and asymmetric C 1s for CaC₆, suggesting the existence of conduction electrons derived from Ca 3d and a charge transfer from Ca to graphene layer. These results provide spectroscopic evidence for PDOS of Ca 3d at E_F. From a comparison of electronic structure of CaC₆ and other graphite intercalation compounds (GICs), we found the difference between CaC₆ and other superconducting GICs, which provides deeper understanding of the superconductivity of CaC₆.     

Adsorption of NH3 and NO2 molecules on C48B6N6 heterofullerene: A DFT study on electronic properties

Adsorption of NH₃ and NO₂ molecules on the external surface of C₄₈B₆N₆ heterofullerene is investigated using DFT method. Attachment of NH₃ and NO₂ on C₄₈B₆N₆ heterofullerenes are compared with the bare C₄₈B₆N₆ model optimized at the B3LYP/6-31G^? level. The high surface binding energies indicates that ammonia undergoes chemical adsorption and could be compatible with the long recovery time but C₄₈B₆N₆ should be good NO₂ sensors with quick response as well as short recovery time. Total (TDOS) and partial (PDOS) density of state calculations is also considered to elucidate the difference in the NH₃ and NO₂ gas detection mechanism of C₄₈B₆N₆. The overlap population density of state (OPDOS) indicated that the chemical adsorption is due to the overlap of atomic orbitals below the Fermi level. The calculated results suggest that the C₄₈B₆N₆ heterofullerene is a suitable sensor material for NO₂ and is an ideal material for elimination and filtering of ammonia.     

Continuous-wave CO2 laser spectroscopy of SF6, WF6, and UF6

The linear absorption of CO₂ laser radiation in SF₆, WF₆, and UF₆ has been measured by using optoacoustic detection techniques. Absolute absorption coefficients per Torr as low as 1 × 10^?7 cm^?1 Torr^?1 in a 2-cm active path length could be measured by taking advantage of calibration measurements performed with SF₆.     

Surface gap and surface electronic states in CuGeO3 single crystal

The surface and bulk electronic excitations of CuGeO₃ are investigated by means of electron energy loss and polarized X-ray absorption spectroscopy. CuGeO₃ shows a surface charge transfer gap of about 3.0±0.3 eV. The unoccupied oxygen derived density of states, as probed by X-ray absorption at the O 1s edge, is in good agreement with recent many-body calculations.     

Low temperature thermoelectric power of LaB6, PrB6 and NdB6

We have measured the thermoelectric power of LaB₆, PrB₆ and NdB₆ in the temperature range 2–20K. PrB₆ and NdB₆ order antiferromagnetically at T_N = 6.99K and 7.74K respectively, whereas LaB₆ is non-magnetic. The thermoelectric power data have a negative maximum near 5.5K in all three hexaborides. This negative peak is thought to be mainly due to phonon drag in LaB₆. In PrB₆ and NdB₆ there is an additional contribution due to magnon drag. It is expected that the high temperature thermoelectric power is mainly due to an electron diffusion term and a contribution due to spin disorder scattering. The thermoelectric power and the resistivity have been compared in the vicinity of T_N. A qualitative similarity in the temperature derivatives of these two quantities has been found for PrB₆ and NdB₆ near T_N.     

Microwave spectrum of the ν5 and ν6 vibrationally excited states of HDCO

Thirty-four transitions belonging to the ν₅ and ν₆ vibrationally excited states of HDCO have been identified in the 10- to 270-GHz region. These two states are strongly coupled by a Coriolis resonance. A set of parameters is obtained using a numerical analysis taking into account the Coriolis coupling.     

Absorption spectra of C6H6 and C6D6 near 340 nm

The absorption spectra of C₆H₆ and C₆D₆ in the liquid phase have been studied near 340 nm. The absorption spectrophotometric mounting was a sequential double-beam attachment with linear response to energy on scanning of the spectrum before the exit slit and an electronic device which gives directly either the absorbance or the integrated absorbance of a transition and, consequently, its oscillator strength.The oscillator strength measured for the band of C₆H₆ is 8×10^?8, which corresponds to a dipole moment of 2.4×10^?3 Debye; this value is of the same order as a theoretical value calculated by Tsubomura and Mulliken (3.8×10^?3 Debye) for a transition between states ³F and ³A of an oxygen-benzene pair. This agreement corroborates the hypothetical existence of such a transition.The first vibrational band is at 28553 cm^?1 for C₆H₆; this band is not observed in the vapor or solid phase. It corresponds probably to the transition 0-0, which is considered in the literature to be near 29500 cm^?1. The isotopic shift measured for this first band is 164 cm^?1. The vibrational frequencies are, respectively, 910 cm^?1 for C₆H₆ and 889 cm^?1 for C₆D₆.     

The magnetic structure of Cs0.4 Mn0.4 Fe1.6 F6 and of Cs0.4 Ni0.4 Fe1.5 F6

The magnetic structure of the two compounds as determined by neutron diffraction is reported. Both compounds are antiferromagnetic with Néel-temperatures of 115 and 100 K respectively. Both compounds show a very pronounced diffuse scattering.     

Higher overtones of the bending vibrations of the ground states of 12CS2 and 13CS2

Large numbers of ‘hot’ bands in the first electronic absorption systems of ¹²CS₂ and ¹³CS₂ have been analyzed from plates taken at high dispersion, and accurate rotational constants have been obtained for the overtones of the ground state bending vibration up to v₂ = 6 and l = 3 for ¹²CS₂ and v₂ = 4, l = 2 for ¹³CS₂. The energy differences between the various levels with the same l value have been determined to an accuracy of about ±0.006 cm^?1, but (because of the parallel polarization of the electronic transition) the absolute energies of levels with l > 0 cannot be obtained.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.     

Spectroscopic and molecular properties of 14 selected electronic states of Si2 molecule

The potential energy curves (PECs) of the X³Σ_g⁻, D³Π_u, a¹Δ_g, b¹Π_u, H′³Σ_u⁻, K³Σ_u⁻, 1³Σ_u⁺, 1³Π_g, 2³Σ_u⁺, 2³Π_g, 3³Π_g, 3³Σ_u⁺, 2³Π_u and 2³Σ_g⁻ electronic states of the Si₂ molecule are investigated using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach with the correlation-consistent basis sets of Dunning and co-workers. The effects on the PECs by the core-valence correlation and relativistic corrections are included. The way to consider the relativistic correction is to use the third-order Douglas-Kroll Hamiltonian approximation. The core-valence correlation correction is made with the aug-cc-pCV5Z basis set. And the relativistic correction is performed at the level of cc-pV5Z basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). The PECs of all these electronic states are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. Using the PECs, the spectroscopic parameters are determined and compared with those reported in the literature. With these PECs determined by the MRCI+Q/CV+DK+56 calculations, the vibrational levels and inertial rotation constants of the first 20 vibrational states are evaluated and compared with the RKR data for these electronic states when the rotational quantum number J equals zero. On the whole, as expected, the most accurate spectroscopic parameters and molecular constants of the Si₂ molecule are determined by the MRCI+Q/CV+DK+56 calculations. And the spectroscopic parameters of the 1³Σ_u⁺, 1³Π_g, 2³Σ_u⁺, 2³Π_g, 3³Π_g, 3³Σ_u⁺, 2³Π_u and 2³Σ_g⁻ electronic states obtained by the MRCI+Q/CV+DK+56 calculations should be good prediction for future laboratory experiment.     

Luminescence of Pr-doped LiCaAlF6 and LiSrAlF6 crystals

The spectral and kinetic parameters of LiCaAlF₆:Pr and LiSrAlF₆:Pr single crystals are studied at LHeT and room temperature (RT). Photon cascade emission (PCE), i.e., ¹S₀→¹I₆ and ³P₀→³H_j, ³F_j transitions after Pr³⁺ excitation via 4f²→4f 5d absorption results in the conversion of the vacuum ultraviolet photon to two visible photons. The excitation and photoemission spectra as well as decay times have been measured and compared with those for CaF₂:Pr and SrF₂:Pr crystals. X-ray luminescence was measured to study the emission origin from both ¹S₀ and ³P₀ states of Pr³⁺. An intense phosphorescence of LiSrAlF₆:Pr was observed in the visible range after X-irradiation at RT, contrary to LiCaAlF₆:Pr.     

The forbidden far-infrared ν6 band of SF6

The far infrared spectra of SF₆ in the 33-μm region in the gas phase at different pressures and in the liquid phase have been studied. A small band situated at 351 cm^?1 on the high-frequency side of two difference bands situated at 304.5 cm^?1 has been observed in the gas phase. Since the integrated intensity of the 351-cm^?1 band varies linearly with the density, it cannot be collision induced. It appears that it is the forbidden ν₆ band that becomes active by Coriolis interaction. This band is seen in the liquid at about the same frequency when it is deconvoluted from the neighboring broadened and split difference bands.     

Interfacial electronic states of an anthracene derivative deposited on a SiO2 /Si substrate

The interfacial electronic states of an anthracene derivative (9,10-bis (methylthio) anthracene) on a SiO₂/Si(100) substrate were studied using ultraviolet photoelectron spectroscopy (UPS). From the UPS measurements, the work function of the sample surface was found to decrease with increasing molecular coverage in the sub-monolayer range. It is concluded that an interfacial electronic dipole (about 0.34 eV) forms at the molecule/ SiO₂ interface and decreases the effective work function.     

The electronic structure of CeO2 and PrO2

We have determined the electronic structure of CeO₂ and PrO₂ by performing SCF band calculations. We find that in both systems there are metal f- and d- electrons in the oxygen 2p bands. We discuss the question of valency and ionicity in these systems.     

The 3ν3 overtone bands of UF6 and UF6

The absorption specta of CO laser radiation by 3ν₃ overtone bands of ²³⁸UF₆ and ²³⁵UF₆ has been measured using photoacoustic spectroscopic techniques. For the two temperatures 250 K and 290 K, measured absorption coefficients and cross-sections of the 3ν₃ band of ²³⁵UF₆ are reported for the first time.