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1.
The absorption and circular dichroism spectra of (-)d-1,12-dimethyl-benzo[c]phenanthrene-5-acetic acid are reported, together with the polarized excitation and fluorescence spectra of the parent hydrocarbon, [4]-helicene. The transition energies of 1,12-dimethyl-[4]-helicene calculated in the π-SCF approximation, and the corresponding dipole and rotational strengths obtained by the dipole-velocity method, show that the optical isomer studied has the M-configuration with the stereochemical form of a segment of a left-handed helix. Analogous calculations in the INDO approximation using both the dipole-velocity and the dipole-length procedure with separate consideration of the one-centre and the two-centre transition moment integrals, indicate that the more satisfactory dipole and rotational strengths are obtained in the two-centre dipole-velocity formulation. The appearance of σ → π* transitions at higher energies limits the application of the π-SCF procedure, but the INDO method is found to place these transitions at too low an energy. 相似文献
2.
Low temperature Mössbauer spectra and magnetic ordering of lithiated ferric molybdate: Li2Fe2(MoO4)3
Powder x-ray diffraction, variable temperature magnetic susceptibility, and zero field Mössbauer spectroscopy measurements were used to characterize the new phase Li2Fe2 (MoO4)3. This material is obtained topochemically simply by the mixing of solutions of lithium iodide in acetonitrile with solid Fe2(MoO4)3 at ambient temperature. Li2Fe2(MoO4)3 possesses the high temperature orthorhombic ferric molybdate $$\begin{gathered} Fe_2 (MoO_4 )_3 + 2LiI\xrightarrow{{CH_3 CN}}Li_2 Fe_2 (MoO_4 )_3 + I_2 \hfill \\ (solid)(solution)(solid)(solution) \hfill \\ \end{gathered}$$ structure. Guinier photographs were completely indexed in space group Pnca. Magnetic hyperfine splitting of the zero field Mössbauer spectrum below 12.5 K indicates a three-dimensional magnetically ordered state which susceptibility results show to be weakly ferromagnetic owing to probable canting of antiferromagnetically coupled sublattices. 相似文献
3.
E. A. Radzhabov 《Optics and Spectroscopy》2014,116(5):769-772
The structure of the absorption spectra of Ce3+, Pr3+, and Tb3+ ions in the vicinity of 4f-5d transitions has been investigated. At low temperatures the absorption spectra exhibit a weakly pronounced fine structure, in contrast to narrow-line spectra in crystals of Ca, Sr, and Ba fluorides. The spectra of Ce3+, Pr3+, and Tb3+ ions in CdF2 can be considered as the absorption spectra of these ions in alkali-earth fluorides, broadened by 60–75 cm?1. The broadening is related to the autoionization of electron from the local 5d(e g ) level to the energy-degenerate states of the conduction band of CdF2 crystal. 相似文献
4.
《Physics letters. A》1987,124(8):463-468
Comparison of UPS (XPS) and XES spectra for the high Tc superconductor La2−xMxCuO4 - calculated using highly precise local density results - with available experimental data reveals a large shift of about 2 eV to lower energies for the Cu-d related features. This shift is interpreted qualitatively in terms of a simple two-level model taking into account the hole-hole repulsion at the Cu sites in the photoemission final state. This simple model explains nicely the magnitude of the shift, the occurence of a Cu related satellite below the valence-bands, and the charge-transfer screening of the Cu-d photo-holes by O-p electrons. The O-states, especially the bonding states at the bottom of the valence band, are less affected and agree reasonably well with the experimental findings. 相似文献
5.
Yu. E. Kitaev T. I. Maksimova K. Hermanowicz M. Mączka J. Hanuza 《Optics and Spectroscopy》2014,116(6):858-863
In a broad temperature range of 4–300 K, we have performed a complex combined investigation of phase transitions in crystals of a ferroelastic K3Na(CrO4)2:MnO 4 2? using methods of Raman light scattering and IR light absorption. Considerable changes that we have observed in both Raman and IR spectra in the range of T ≈ 150 K testify to the occurrence of another phase transition that has not been observed before at this temperature. We have performed a group-theoretical analysis and compared its results with experimental spectra, which has allowed us to conclude that there are two phase transitions in this crystal, \(P\bar 3m1 \to C2/m \to C2/c\) , which occur at temperatures T c1 ≈ 230 K and T c2 ≈ 150 K, respectively. 相似文献
6.
Synthesis, MSssbauer Spectra and Magnetic Properties of Quasi-One-Dimensional Fe3O4 Nanowires
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Quasi-one-dimensional Fe3O4 nanowires in diameter of about 200nm were assembled into anodic aluminium oxide templates via electrodepositing and heat-treating processes. The nanowires have a polycrystalline spinel structure with α=8.317А, and each nanowire is composed of fine Fe3O4 crystallites with size of about 30nm. 相似文献
7.
P. Thakur J. C. Cezar N. B. Brookes R. J. Choudhary D. M. Phase K. H. Chae Ravi Kumar 《Hyperfine Interactions》2010,197(1-3):95-100
The electronic and magnetic properties of well characterized Mo1???xFexO2 (x = 0–0.5) thin films that show ferromagnetism at room temperature (RT) have been investigated by the means of near edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments at the O K-, Fe L-, and Mo M-edges. The NEXAFS spectra at O K- and Mo M3,2 -edges show a strong hybridization of O 2p-4d Mo orbitals, and Mo ions change their symmetry with the substitution of Fe ions into MoO2 matrix. The Fe 2p NEXAFS/XMCD spectra exhibit multiple absorption peaks and an appreciable XMCD signal that persists even at RT. These results demonstrate that Fe is in a mixed valence state of Fe2?+?–Fe3?+?, substituting at the Mo site and that the Fe2?+?/3?+? ions are ferromagnetically polarized. 相似文献
8.
《Journal of Molecular Spectroscopy》1986,119(1):51-55
Pure quadrupole transitions of the iodine nucleus in CH2DI have been measured by laser-radio frequency double resonance, and analyzed to yield quadrupole coupling constants in the ground, v6 = 1 and v3 = 2 states. The corresponding infrared spectra, which were required in order to make assignments, have also been analyzed using Fourier transform data at a resolution of about 0.05 cm−1. 相似文献
9.
K. Karoui M. Ben Bechir A. Ben Rhaiem A. Bulou F. Calvayrac K. Guidara 《Phase Transitions》2013,86(6):613-628
The infrared and Raman spectra of [N(CH3)4]2ZnCl4?yBry, where y = 0, 2 and 4, have been analyzed with ab initio calculations of the vibrational characteristics of constitutive polyhedra, tetramethylammonium [N(CH3)4]+ and [ZnCl4?xBrx]2? (x = 0, 1, 2, 3 and 4) tetrahedra. The optimized geometries, calculated vibrational frequencies, infrared intensities and Raman activities are calculated using Hartree–Fock and density functional theory B3LYP methods with 3-21G, 6-31G(d) and 6-311G+(d,p) basis sets. Calculation of the root mean square difference δrms between the observed and calculated frequencies allows to give scaling factors and to deduce that the best agreements are obtained by B3LYP/6-311G+(d,p) for [N(CH3)4]+ and B3LYP/3-21G for [ZnCl4?xBrx]2?. The present study establishes a strongly reliable assignment of the vibrational modes of [ZnCl4?xBrx]2? tetrahedra based on comparison between experimental and ab initio calculations, both of the frequencies and the intensities of the Raman signals. 相似文献
10.
《Applied Surface Science》2001,169(1-2):72-78
MoS2, Co–MoS2 and K2CO3/Co–MoS2 catalysts have been characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD analysis indicates that Co–MoS2 is a primary phase in K2CO3/Co–MoS2 catalyst and the diffraction lines of Co–MoS2 are not changed by the addition of K2CO3. Co9S8 phase is not present at Co/Mo mole ratio of 0.5 using a co-precipitation method for preparation of cobalt–molybdenum catalyst. The binding energies (BEs) of chemical species present on the surface of the catalysts are compared through the course of catalyst preparation. K2CO3/Co–MoS2 catalyst has been investigated as a function of dispersion of K on the surface and exposure to a mixture of carbon monoxide and hydrogen (syngas) by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The distribution of potassium on the surface of the K-promoted catalyst is not uniform. 相似文献
11.
The (2)H(d,p)(3)H, (2)H(d,n)(3)He, and (2)H(d,γ)(4)He reactions are studied at low energies in a multichannel ab initio model that takes into account the distortions of the nuclei. The internal wave functions of these nuclei are given by the stochastic variational method with the AV8' realistic interaction and a phenomenological three-body force included to reproduce the two-body thresholds. The obtained astrophysical S factors are all in very good agreement with the experiment. The most important channels for both transfer and radiative capture are identified by comparing to calculations with an effective central force. They are all found to dominate thanks to the tensor force. 相似文献
12.
The 2H(d, γ)4He capture reaction and the 2H(d, p)3H and 2H(d, n)3He transfer reactions at very low energies are studied in an extended microscopic cluster model with a realistic nucleon–nucleon force. Our results show that the tensor force in realistic interactions plays an essential and indispensable role to reproduce the very low-energy astrophysical S factor of these reactions. 相似文献
13.
14.
《Journal of Molecular Spectroscopy》1987,125(2):309-331
The infrared spectrum of the ν4(E) and 2ν2(A1) bands of 12CD3F have been recorded and deconvolved to ∼0.005 cm−1 resolution. More than 1890 transitions have been assigned to one of the 37 subbands (−18≤KΔK≤+18) comprising the spectrum of the ν4 band with a maximum assigned J value of 41. The weak 2ν2(A1) band has never been reported in the infrared prior to this work. A total of 358 transitions in K ≤ 8 subbands have been assigned to the 2ν2 band. The two bands are members of the 24 interacting state complex of 12CD3F spectra in the 5-μm region. The ν4 and 2ν2 spectra are highly perturbed, exhibiting local and global resonances. Effective parameters of the two bands were obtained by fitting the data in a restricted manner leaving out the obviously perturbed transitions. The effective parameters, the identification of the different resonances affecting the bands, and estimates of some of the coupling constants are reported. 相似文献
15.
W.-L. Feng 《Optik》2009,120(14):696-2699
In this paper, the optical absorption spectra of Yb3+ in the α-Al2O3 crystal are reasonably explained by using the superposition model and local lattice structure analysis. Based on these studies, we find that the local geometrical structure around the Yb3+ ions possesses an elongated trigonal distortion above the O2−-triangle and a compressed trigonal distortion in the lower one. 相似文献
16.
A method for exploring Jahn—Teller systems in the framework of Density Functional Theory is described in the present work. Using such a method the properties of the Rh2? centre in NaCl with remote charge compensation are studied. The calculations support the existence of a strong Jahn—Teller effect and account reasonably for the main features of EPR and optical spectra. The onset of charge transfer excitations is calculated to be at about 3.7 eV a fact which concurs with available experimental data. The elongated geometry is found to be about 200cm?1 more stable than the compressed one in agreement with experiments. 相似文献
17.
Takashi Yamamoto 《X射线光谱测定》2008,37(6):572-584
The characteristics of pre‐edge peaks in K‐edge x‐ray absorption near edge structure (XANES) spectra of 3d transition metals were reviewed from viewpoints of the selection rule, coordination number, number of d‐electrons, and symmetry of the coordination sphere. The contribution of the electric dipole and quadrupole transition to the peaks was discussed on the basis of the group theory, polarized spectra, and theoretical calculations. The pre‐edge peak intensity for Td symmetry is larger than those for Oh symmetry for all 3d elements. The intense pre‐edge peak for tetrahedral species of 3d transition metals is not due to 1s–3d transition, but transition to the p component in d–p hybridized orbital. The mixing of metal 4p orbitals with the 3d orbitals depends strongly on the coordination symmetry, and the possibility is predictable by group theory. The transition of 1s electron to d orbitals is electric quadrupole component in any of the symmetries. The d–p hybridization does not occur with regular octahedral symmetry, and the weak pre‐edge peak consists of 1s–3d electric quadrupole transition. The pre‐edge peak intensity for a compound with a tetrahedral center changes as a function of the number of 3d electrons regardless of the kind of element; it is maximized at d0 and gradually decreases to zero at d10. The features of pre‐edge peaks in K‐edge XANES spectra for 4d elements and the L1‐edge for 5d elements are analogous with those for 3d elements, but the pre‐edge peak is broadened due to the wide natural width of the core level. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
18.
The pure rotational spectrum of the near-spherical oblate symmetric top AsD3 has been recorded in the 20–120cm?′ region with a resolution of 2.3 × 10?3 m?1 employing an FT interferometer. Rotational transitions with 5 ? J ? 29 and 0 ? X ? 25 of the ground state (GS) and the v2 = 1 and v4 = 1 excited states have been assigned. Splittings were observed for the GS, 98, K = 3 and 6 levels, the K = 3 levels of v2 and the kl = ?2, 1, 4 and 7 levels of v4. Furthermore the x,y Coriolis coupled v2 and v4 bands, v 0 2 = 654.4149cm?1, and v 0 4 = 714.3399 cm?1, have been examined with a resolution of 2.4 × 10?3 cm?1, and ca. 2500 allowed and 336 ‘forbidden’ lines with J′max = 31 and K′max = 28 have been assigned. Appropriately weighted GS data comprising FIR lines, allowed and ‘forbidden’ (up to ΔK = ±6) GS combination differences, mmw data, and ΔJ = 0, ΔK = ±1 distortion moment transitions were fitted together, and GS parameters complete through H parameters have been determined. Two different reductions of the Hamiltonian, either with ΔK = ±6 (h3) or ΔK = ±3 (ε) off-diagonal elements, have been employed. Equivalence of these reductions up to J = 22 was established while for J > 22 the ε reduction is superior. The v2 and v4 data have been fitted with two equivalent models based on different reductions of the rovibrational Hamiltonian. In addition to the dominating x,y Coriolis resonance, ζ y 24 0.520, Δ(k ? l) = ±3 and ±6 interactions are important and were accounted for by the models. The transition moment ratio |M4: M2| =0.75 has been determined, with a positive sign of the product M 2ζ y 24 M 4. An improved r0 structure, r0(AsD) = 1.51753 Å and α0(DAsD) = 92.000°, has been determined. 相似文献
19.
N. N. Sirota I. M. Sirota T. M. Soshnina T. D. Sokolovskii 《Physics of the Solid State》2001,43(9):1743-1749
The dependences of the cohesive (atomization) energy on the interatomic distance for elements Al, Cu, Ti(A2), V, Mg, Ti(A3), Si, and Sn are calculated using methods based on the Thomas-Fermi-Dirac-Gambosh statistical atomic theory. The obtained dependences are approximated by the Mie-Grüneisen potential. The phonon spectra calculated on the basis of the Born-Kärmän model and the Born-Kärmän-Blackman-de Lunay approach are used to determine the temperature dependences of the specific heat, free energy, and internal energy of the elements under investigation. The calculated cohesive energy, equilibrium interatomic distances, and temperature dependences of the specific heat agree with the experimental data. 相似文献
20.
We present results for exclusive semileptonic decay widths of ground state spin-1/2 and spin-3/2 cb baryons corresponding to a c → s, d transition at the quark level. The relevance of hyperfine mixing in spin-1/2 cb baryons is shown. Our form factors are compatible with heavy quark spin symmetry constraints obtained in the infinite heavy quark mass limit. 相似文献