Solvent effects on the S0→S2 absorption spectra of β-carotene

Absorption spectra of β-carotene in 31 solvents are measured in ambient conditions. Solvent effects on the 0-0 band energy, the bandwidth, and the transition moment of the S 0 → S 2 transition are analysed. The discrepancies between published results of the solvent effects on the 0-0 band energy are explained by taking into account microscopic solute-solvent interactions. The contributions of polarity and polarizability of solvents to 0-0 band energy and bandwidth are quantitatively distinguished. The 0-0 transition energy of the S 2 state at the gas phase is predicted to locate between 23000 and 23600 cm-1 .     

HIGH-RESOLUTION ANALYSIS OF THE ν2+2ν3 BAND OF HDO

The Fourier transform spectrum of the ν₂+2ν₃ band of the HDO molecule was recorded with a resolution of 0.02 cm^-1. The spectrum was rotational analysed and the spectroscopic parameters of the (0,1,2) state were estimated in terms of Watson's effective rotational Hamiltonian model and also the model in the Padé-Borel approximation form. They reproduce the upper energy levels with an accuracy close to the experimental uncertainty of 0.001 cm^-1.     

RAMAN SCATTERING OF α-ET3(ReO4)2 CHARGE-TRANSFER SALT

We describe the results of Haman studies on C=C stretch modes in α-ET₃(ReO₄)₂ charge-transfer salt with the incident laser beam polarised perpendicular and parallel to the large flat face of plate-like crystal. We have assigned central C=C stretch mode at 1454 cm^-1 and ring C=C stretch mode at 1470cm^-1. The change in ring C=C stretch vibration was observed at the metal-insulator transition of α-ET₃(ReO₄)₂ on warming due to the distortion of the ET molecules.     

Investigations of spectroscopic parameters and molecular constants for X1Σg+, w3Δu, and W1Δu electronic states of P2 molecule

The potential energy curves (PECs) of three low-lying electronic states (X¹Σ_g⁺, w³Δ_u, and W¹Δ_u)of P₂ molecule are investigated using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in conjunction with the correlation-consistent basis set in the valence range. The PECs of the electronic states involved are modified by the Davidson correction and extrapolated to the complete basis set (CBS) limit. With these PECs, the spectroscopic parameters of the three electronic states are determined and compared in detail with the experimental data. The comparison shows that excellent agreement exists between the present results and the available experimental data. The complete vibrational states are computed for the w³Δ_u, and W¹Δ_u electronic states when the rotational quantum number J equals zero and the vibrational level G(v), the inertial rotation constant B_v, and the centrifugal distortion constant D_v of the first 30 vibrational states are reported, which accord well with the experimental data. The present results show that the two-point extrapolation scheme can obviously improve the quality of spectroscopic parameters and molecular constants.     

CuH分子A1∑+态的寿命和预解离研究

A combined cavity ringdown (CRD) and laser induced fluorescence (LIF) spectroscopic study on the A¹∑⁺-X¹∑⁺ transition of CuH has been presented.The CuH molecule,as well as its deuterated isotopologue CuD,are produced in a supersonic jet expansion by discharging H₂(or D₂) and Ar gas mixtures using two copper needles.Different profiles of relative line intensities are observed between the measured LIF and CRD spectra,providing an experimental evidence for the predissociation behavior in the A¹∑⁺ state of CuH.The lifetimes of individual upper rotational levels are measured by LIF,in which the J''-dependent predissociation rates are obtained.Based on the previous theoretical calculations,a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A¹∑⁺ state and the lowest-lying triplet ³∑⁺ state,and a tunneling effect may also be involved in the predissociation.Similar experiments are also performed for CuD,showing that the A¹∑⁺ state of CuD does not undergo a predissociation process.     

THERMALLY ACTIVATED HOPPING IN Dy1-xPrxBa2Cu3O7-δ SYSTEM

The temperature dependence of resistivity in Dy_1-xPr_xBa₂Cu₃O_7-δ system with x>0.6 was measured. The experimental results show that Pr substitution leads to the localization of mobile holes and such a localization is enhanced with increasing Pr concentration. The gradually enhancing of localization induces Anderson transitions one by one in this system, including the transition from the conduction by excitation of holes to the one by thermal activation hopping between localized states, the so called Anderson transition type-I, and the transition from nearest neighbor hopping (NNH) to variable range hopping (VRH), the Anderson transition type-II, and the Anderson transition type-lI from 3D to 2D.     

ELECTRONIC AND OPTICAL PROPERTIES OF STRAINED WURTZITE GaN

Band structures of wurtzite GaN (α-GaN) under strains in the region -5%—5% are calculated in a tight-binding framework. The empirical scaling rule has been used for considering the effects of hydroatatic strains. The scaling indexes are determined by fitting the deformation-potential constants with other theoretical values. The band gap at Γ point increases with the absolute value of strains. GaN turns to be of indirect band gap when strains reach 5 %. The density of states and the imaginary part of dialectic function (ε₂(ω)) are studied. Both the shape and energy position of the highest peak in the ε₂(ω) spectrum successively change with the strains. The real part of dielectric/unction, refractive index and the effects of the strains on them are also shown.     

THE 82S1/2→62D EXCITATION TRANSFER OF RUBIDIUM ATOMS INDUCED BY COLLISIONS WITH GROUND-STATE RUBIDIUM AND HYDROGEN MOLECULES

The processes of excitation transfer from the 8²S_1/2 state to the 6²D state of rubidium in Rb(8²S_1/2)-Rb(5²S_1/2) and Rb(8²S_1/2)-H₂ collisions have been studied experimentally. During irradiating the Rb vapor, mixed with H₂, by two light beams for selective stepwise excitation, the Rb 8²S_1/2→5²P_3/2 direct fluorescence and the Rb 6²D_3/2→5²P_1/2 sensitized fluorescence have been measured as a function of H₂ gas pressure. The measurements yielded the cross-sections σ(8²S_1/2→6²D) and σ^*(8²S_1/2→6²D) of Rb 8²S_1/2→6²D excitation tranfer induced by collisions with 5²S_1/2 atom and H₂ molecules respectively. The results are discussed in detail.     

THE 82S1/2→62D EXCITATION TRANSFER OF RUBIDIUM ATOMS INDUCED BY COLLISIONS WITH GROUND-STATE RUBIDIUM AND HYDROGEN MOLECULES

The processes of excitation transfer from the 8²S_1/2 state to the 6²D state of rubidium in Rb(8²S_1/2)-Rb(5²S_1/2) and Rb(8²S_1/2)-H₂ collisions have been studied experimentally. During irradiating the Rb vapor, mixed with H₂, by two light beams for selective stepwise excitation, the Rb 8²S_1/2→5²P_3/2 direct fluorescence and the Rb 6²D_3/2→5²P_1/2 sensitized fluorescence have been measured as a function of H₂ gas pressure. The measurements yielded the cross-sections σ(8²S_1/2→6²D) and σ^*(8²S_1/2→6²D) of Rb 8²S_1/2→6²D excitation tranfer induced by collisions with 5²S_1/2 atom and H₂ molecules respectively. The results are discussed in detail.     

一氧化二氮分子位于775 nm的6υ3振动泛频跃迁的高精密光腔衰荡光谱

Transitions of the 6υ₃ overtone band of ¹⁴N₂ ¹⁶O near 775 nm have been studied by continuous-wave cavity ring-down spectroscopy. Line positions and intensities were derived from a fit of the line shape using a hard-collisional profile. The line positions determined with absolute accuracy of 5×10^-4 cm^-1 allowed us to reveal finer ro-vibrational couplings taking place after J>14 except a strong anharmonic interaction identified by the effective Hamiltonian model. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for a majority of the unblended lines. A new set of ro-vibrational and dipole moment parameters were derived from the experimental values. A comparison between the line positions and intensities of the 6υ₃ band obtained in this work and those from previous studies is given.     

Eu3+离子对Li2O-Na2O-B2O3物理和光学特性的影响

The lithium sodium borate glasses doped with Eu³⁺ ion are prepared using melt quenching technique, their structural and optical properties have been evaluated. The density of prepared glasses exhibits an inverse behavior to the molar volume ranging from 2.26 g/cm³ to 2.43 g/cm³ and 26.95 cm³ /mol to 26.20 cm³ /mol, respectively. The absence of sharp peaks in XRD patterns confirms the amorphous nature of the prepared glasses. The absorption spectra yield four transitions centered at 391 nm (⁷F₀→⁵L₆), 463 nm (⁷F₀→⁵D₂), 531 nm (⁷F₀→⁵D₁), and 582 nm (⁷F₀→⁵D₀). The most intense red luminescence is observed at 612 nm corresponding to ⁵D₀→⁷F₂ transition under 390 nm laser excitations.     

Ar原子偶宇称3p5(2P1/2)nl'[K']J(l'=1,3)自电离态激发谱线形研究

The even-parity autoionizing resonance series 3p⁵np''[3/2]_1,2, 3p⁵np''[1/2]₁, and 3p⁵nf''[5/2]₃ of Ar have been investigated exciting from the two metastable states 3p⁵4s[3/2]₂ and 3p⁵4s''[1/2]₀ in the photon energy range of 32500-35600 cm^-1 with an experimental bandwidth of ~0.1 cm^-1. The excitation spectra of the even-parity autoionizing resonance series show typical asymmetric line shapes. New level energies, quantum defects, line profile index and resonance widths, resonance lifetime and reduced widths of the autoionizing resonances are derived by a Fano-type line-shape analysis. The line profile index q and the resonance widths Γ are shown to be approximately proportional to the effective principal quantum number n^*. The line separation of the 3p⁵np'' autoionizing resonances is discussed.     

LECTRONIC STRUCTURE STUDIES OF Bi2Sr2CaCu2-xSnxO8+δ SYSTEM

Photoemission measurements have been carried out for Bi₂Sr₂CaCu_2-xSn_xO_8+δ system with conventional x-ray photoemission spectroscopy for core-level spectra and synchrotron radiation photoemission spectroscopy for valence band. With Sn doping, all core levels shift differently in binding energy, and the intensity near fermi energy becomes smaller in valence hand. From the experiment, we can deduce that the shifts of all core levels and valence hands may involve some other mechanisms, such ms electrostatic effects, in addition to binding energy referencing effects. We argue that the chemical environment plays a crucial role in the electronic structure of high-temperature superconductors.     

OPTICAL PROPERTIES OF δ-DOPED GaAs AND GaAs/Al0.1Ga0.9As SUPERLATTICES

Radiative transition in δ-doped GaAs superlattices with and without Al_0.1Ga_0.9As barriers is investigated by using photoluminescence at low temperatures. The experimental results show that the transition mechanism of δ-doped superlattices is very different from that of ordinary superlattices. Emission intensity of the transition from the electron first excited state to hole states is obviously stronger than that from the electron ground state to hole states due to larger overlap integral between wavefunctions of electrons in the first excited state and hole states. Based on the effective mass theory we have calculated the self-consistent potentials, optical transition matrix elements and photoluminescence spectra for two different samples. By using this model we can explain the main optical characteristics measured. Moreover, after taking into account the bandgap renormalization energy, good agreement between experiment and theory is obtained.     

PuO分子X5Σ-态的势能函数及热力学 函数的量子力学计算

The potential energy function for ground state X⁵Σ^- of the PuO molecule was worked out by the quadratic configuration interaction of single and double substitution method, based on the approximation of relativistic effective core potential for Pu atom and all-electron 6-311G^ basis set for O atom. The calculated results for R_e,D_e,B_e,α_e,ω_e and ω_eχ_e are 0.183nm,7.3909eV,0.3365,0.001642,781.15,and 2.77cm^-1,respectively.In addition,the thermodynamic functions ΔH⁰,ΔS⁰,ΔG⁰ and C_p of the PuO(g) in standard state are also calculated,which are -118.88kJ/mol,96.16J/mol^.K,-147.55kJ/mol,and 31.5656J/mol^.K,respectively. All these results are in good agreement with the experimental data.     

Intense up-conversion emissions of Yb3+/Dy3+ co-doped Al2O3 nanopowders prepared by non-aqueous sol—gel method

Yb³⁺/Dy³⁺ co-doped Al₂O₃ nanopowders have been prepared by the non-aqueous sol-gel method and their up- conversion photoluminescence spectra are measured under excitation by 980-nm semiconductor laser. The results show that there are comparatively abundant spectra of up-conversion emissions centered at 378, 408, 527 and 543, and 663 nm, corresponding to ⁴G_9/2 → ⁶H_13/2, ⁴G_9/2 → ⁶H_11/2, ⁴I_15/2 → ⁶H_13/2, and ⁴F_9/2 → ⁶H_11/2 transitions of Dy³⁺, respectively. Two-photon and three-photon processes are involved in ultraviolet, violet, green, and red up-conversion emissions. The energy transition between Yb³⁺ and Dy³⁺ is discussed.     

INFLUENCE OF γ-RADIATION ON THE DIELECTRIC CHARACTERISTICS IN Rb2ZnCl4 SINGLE CRYSTALS AT INCOMMENSURATE-COMMENSURATE PHASE TRANSITION

In this paper the influence of γ-radiation on the dielectric constants of Rb₂ZnCl₄ crystal at incommensurate-commensurate phase transition (hereafter abbreviated as INC-C transition) are studied. The thermal hysteresis occurs upon both cooling and heating runs, irrespective of whether the samples have been treated with γ-radiation or not. For the γ-irradiated sample, its transition point, T_c, between the INC and C phases is not changed, but the peak value of the dielectric constant at T_c increases abruptly, compared with that before γ-irradiation, When this sample is annealed at 40℃, the peak value restores to the incipient value for the sample free from γ-irradiation. The origin of the phenomenon of the thermal hysteresis of the dielectric constant may be due to the pinning effect of dejects or impurities in the samples.     

丙烷与O(3P)反应机理和动力学的理论研究

The reaction of C₃H₈+O(³P)→C₃H₇+OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Møller-Plesset perturbation method and the single-point energy is computed using the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C₃H₈+O(³P)→i-C₃H₇+OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present work reveals the reaction mechanism of hydrogen-abstraction from propane involving reaction channel competitions is helpful for the under-standing of propane combustion.     

VIOLET LIGHT-EMISSION FROM Ge+-IMPLANTED SiO2 FILMS ON Si SUBSTRATE

Germanium ions were implanted into SiO₂ films which were thermally grown on crystalline Si at an energy of 60 keV and with doses of 1×10¹⁵ and 1×10¹⁶ cm^-2.Under an ultraviolet excitation of ～5.0 eV,the implanted f ilms annealed at various temperatures exhibit intense violet luminescence with a peak at 396 nm.It is ascribed to the T₁→S₀ transition in GeO,which was formed during implantation and annealing process.     

The effect of anti-hydrogen bond on Fermi resonance: A Raman spectroscopic study of the Fermi doublet ν1—ν12 of liquid pyridine

The effects of anti-hydrogen bond on the ν₁—ν₁₂ Fermi resonance (FR) of pyridine are experimentally investigated by using Raman scattering spectroscopy. Three systems, pyridine/water, pyridine/formamide, pyridine/carbon tetrachloride, provide varying degrees of strength for the diluent-pyridine anti-hydrogen bond complex. Water forms a stronger anti-hydrogen bond with pyridine than with formamide, and in the case of adding non-polar solvent carbon tetrachloride, which is neither a hydrogen bond donor nor an acceptor and incapable of forming hydrogen bond with pyridine, the intermolecular distance of pyridine will increase and the interaction of pyridine molecules will reduce. The dilution studies are performed on the three systems. Comparing with the values of Fermi coupling coefficient W of the ring breathing mode ν ₁ and triangle mode ν ₁₂ of pyridine at different volume concentrations, which are calculated according to the Bertran equations, in three systems, we find that the solution with the strongest anti-hydrogen bond, water, shows the fastest change in the ν₁—ν₁₂ Fermi coupling coefficient W with the volume concentration varying, followed by the formamide and carbon tetrachloride solutions. These results suggest that the stronger anti-hydrogen bond-forming effect will cause a greater reduction in the strength of the ν₁—ν₁₂ FR of pyridine. According to the mechanism of the formation of anti-hydrogen bond in the complexes and the FR theory, a qualitative explanation for the anti-hydrogen bond effect in reducing the strength of the ν₁—ν₁₂ FR of pyridine is given.