分子超激发态的理论研究:F2分子离子对解离效率谱的标识及强度

在量子数亏损理论框架下,应用多重散射自洽场方法和含时波包演化法研究了F2分子经过超激发态发生离子对解离产生的F-离子产生效率谱.根据我们的计算,可以给出清楚的标识,并且对实验谱的相对强度可以给出初步说明.     

分子超激发态结构的理论研究:F2离子对解离效率谱研究

在量子数亏损理论框架下,利用多重散射自洽场方法和Feynman传播子算法研究了高分辨的F2分子超激发态结构;该超激发态能够解离为正负离子对F^＋（^3P2,1,0）＋F^-（^1S0）.理论分析能够清楚地标识其振动分辨谱,并很好地与实验测量符合.文章还阐述了发展分子超激发态结构研究的前景.     

Ar2+与Li,Na原子碰撞中单电子俘获过程的实验研究

对Ar²⁺与Li,Na碰撞过程中由于单电子俘获而产生的ArII谱线进行了绝对测量,给出各谱线的发射截面数据。入射离子能量为40—300keV。从发射截面对势能亏损的依赖关系,发现对应中等△E(>0)值的过程具有较大的截面。并且还发现与观察到的光谱线相应的激发态属于一个电子组态中高J量子数的态。 关键词：     

离化态原子的激发态结构

本文根据相对论性自洽场理论,计算了原子序数从2到95的各种离化态原子激发态能级,从而总结了s,p,d,f和g通道的量子数亏损。阐明了量子数亏损随着原子序、电离度(或电子占有数)和电子轨道能量变化的规律。在此基础上可以建立离化态原子激发态量子数亏损数据库。 关键词：     

铅原子奇宇称Rydberg系列寿命的研究

在多通道量子数亏损理论(MQDT)的基础上,利用已给出的用MQDT波函数统一计算高激发态寿命的方法,计算并预言了J=1奇宇称两个Rydberg系列的寿命,在利用MQDT计算时,确定了6p6d3/2[3/2]₁⁰的能级位置.     

量子数亏损理论——多重散射计算方法

将多重散射自洽场方法和多通道量子数亏损理论结合,计算出分子的相互作用自洽势,对分子丰富的高激发态以及相应的连续态——分子的电离通道进行计算和分析,并给出了H₂,NO等分子的计算例子。 关键词：     

Ar~(2 )与Li,Na原子碰撞中单电子俘获过程的实验研究

对Ar~(2 )与Li,Na碰撞过程中由于单电子俘获而产生的Arll谱线进行了绝对测量,给出各谱线的发射截面数据。入射离子能量为40—300keV。从发射截面对势能亏损的依赖关系,发现对应中等△E(>0)值的过程具有较大的截面。并且还发现与观察到的光谱线相应的激发态属于一个电子组态中高J量子数的态。     

以Ne原子为联合原子的系列分子里德伯能级结构

本文在独立电子近似的基础上,利用多重散射自洽场理论方法,系统地计算了含10个电子的分子B₂,HF,H₂O,NH₃,CH₄的里德伯能级结构,通过分析这些分子量子数亏损的变化规律,阐明了其激发态的电子能级结构,根据分子电子组态的联合原子极限,确定了各里德伯初始态的主量子数,量子数亏损的计算值与已有的实验值符合良好。 关键词：     

弯曲振动对CS_2分子~1B_2(~1Σ_u~+)态预解离寿命的影响

在209.5～216nm,采用光解碎片激发(PHOFEX)谱技术,对CS2分子1B2(1Σ+u)态预解离寿命进行了 考察.测量在超声射流中进行.信号来自解离碎片CS(A1Π,v′=0←X1Σ+,v″=0)Q支带头的激光诱导荧光 (LIF).预解离寿命是通过对谱带进行拟合来提取的.拟合中假定基态转动布居为Boltzmann分布,寿命加宽的转 动谱线为Lorentz线形.通过拟合共获得1B2(1Σ+u)态13个跃迁所对应的预解离寿命,其中6个数据是新得到的. 结果表明,基态振动角动量量子数l或激发态转动角量子数K(K=l)对预解离寿命有明显的影响.对于激发态的 同一振动能级,较大的K对应于较短的预解离寿命.实验中采用可加热的射流喷嘴,用以提高热带激发的强度, 以改善对较大转动角量子数K的影响的考察.     

超冷铯分子0g-长程态的振转光谱研究

通过超冷铯原子光缔合制备激发态的超冷铯分子. 利用冷原子荧光频率调制技术获得了超冷铯分子第一激发态6S_1/2+6P_3/2离解限0_g^-长程态高分辨振转光谱, 计算得到0_g^- 长程态振动量子数从0到51的不同振动能级的转动常数, 和Daniel研究小组的理论结果符合得很好. 关键词： 超冷铯分子 光缔合 振转光谱     

The structure of mixed fluorides Ca1?xSrxF2 and Sr1?xBaxF2 and the luminescence of Eu2+ in these crystals

The structure of the mixed fluorites Ca_1−x Sr_xF₂ and Sr_1−x Ba_xF₂, as well as the structure of the Eu²⁺ impurity center in these crystals, is calculated within the framework of the virtual-crystal method realized in the shell model and pair-potential approximation. The phenomenological dependence of the position of the lower level of the 4f ⁶5d configuration of the Eu²⁺ ion on distance to the Eu²⁺-ligand is derived. The dependences of the Stokes shift and the Huang-Rhys factor on x are calculated for the yellow luminescence in Sr_1−x Ba_xF₂:Eu²⁺. The value of x at which the lower level of the 4f ⁶5d configuration of the Eu²⁺ ion in Sr_1−x Ba_xF₂:Eu²⁺ falls within the conduction band is found. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 5, 2003, pp. 823–826. Original Russian Text Copyright ? 2003 by Nikiforov, Zakharov, Chernyshev, Ugryumov, Kotomanov.     

Studies of the crystal field energy levels and g factors for Ce in LiYF4 crystal

The five observed crystal field energy levels and EPR g factors g_//and g_⊥ for Ce³⁺-doped LiYF₄ crystal are calculated together from a complete diagonalization (of energy matrix) method. In the method, the contributions to g factors of ground Kramers doublet from all the rest doublets within the ground and excited manifolds ²F_5/2 and ²F_7/2 are included. The calculated results show reasonable agreement with the experimental values. The calculations suggest that the crystal field parameter B₂₀ > 0 in LiYF₄: Ce³⁺ crystal. The opinion of the parameter B₂₀ < 0 in the previous paper is not correct. Since this opinion is based on the calculation of g factors using a very simple method where only the contributions to g factors from the doublets within the ground manifold ²F_5/2 are considered, it is suggested that this simple method is not effective in the calculation of g factors for 4f¹ ions in crystals.     

Yb3+:Gd2SiO5晶体的结构和光谱性能

采用提拉法成功生长尺寸为φ30 mm× 75 mm的15at.%Yb³⁺:Gd₂SiO₅单晶, 并用Reitveld全谱拟合方法确定了其晶格常数、原子坐标和温度因子等参数. 用吸收光谱计算了Yb³⁺离子²F_7/2↔ ²F_5/2能级跃迁的振子强度、谱线强度、跃迁概率、 能级寿命和积分发射截面等光谱参数, 并根据激光性能评估得出结论: 表明该晶体具有较大的阈值特性, 有望采用大功率激光二极管泵浦实现可调谐或超快激光输出.     

First-principles electronic-structure calculation on the spin distribution and the half-metallic properties of the mixed valence iron compound Ba2F2Fe1.5S3

The first principles within the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) approach were applied to study the new mixed valence compound Ba₂F₂Fe_1.5S₃. The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that the compound has an antiferromagnetic interaction between the Fe^III and Fe^II ions arising from the bridging S atoms, which validate the experimental assumptions that there is a low-dimensional antiferromagnetic interaction in Ba₂F₂Fe_1.5S₃. The spin magnetic moment mainly comes from the Fe^III and Fe^II ions with smaller contribution from S anion. By analysis of the band structure, we find that the compound has half-metallic property.     

IR luminescence of thulium-activated crystals of double sodium yttrium fluoride Na0.4Y0.6F2.2:Tm3+: Self-quenching of luminescence from the 3H4 level

Na_0.4Y_0.6F_2.2:Tm³⁺ crystals with thulium contents of 0.5–20% have been grown by the Stockbarger-Bridgman method. The concentration dependences of the steady-state spectra and luminescence kinetics from the ³ H ₄ and ³ F ₄ thulium levels upon selective laser excitation of a series of Na_0.4Y_0.6F_2.2:Tm³⁺ crystals (0.5–20% Tm) are investigated. It is shown that the luminescence from the ³ H ₄ level becomes significantly quenched with an increase in the concentration due to the nonradiative energy transfer. No concentration quenching of luminescence from the ³ F ₄ level is observed. Possible schemes of self-quenching are considered for the ³ H ₄ thulium level, the self-quenching microparameters and macrorates are estimated using model quantum-mechanical calculation, and the most likely self-quenching mechanisms and schemes are found from comparison of the calculated and experimental self-quenching rates. Good agreement is obtained between the experimental and calculated kinetic curves. It is shown that, under pumping near ∼0.8 μm, self-quenching of the ³ H ₄ thulium level leads to effective occupation of the ³ F ₄ level and increases the luminescence intensity in the range of 1.7–1.9 μm. It is concluded that Na_0.4Y_0.6F_2.2:Tm³⁺ crystals are promising active media for tunable lasers in the range of 1.7–1.9 μm, with small thermal loss under laser-diode pumping near 0.8 μm. Original Russian Text ? S.é. Ivanova, A.M. Tkachuk, A.A. Mirzaeva, F. Pellé, 2009, published in Optika i Spektroskopiya, 2009, Vol. 106, No. 6, pp. 922–930.     

Theoretical calculations of the optical band positions and spin-Hamiltonian parameters for Yb at the tetragonal Y site of KY3F10 crystal

The six optical band positions and six spin-Hamiltonian parameters [g factors g_∥, g_⊥ and hyperfine structure constants A_∥(¹⁷¹Yb³⁺), A_⊥(¹⁷¹Yb³⁺), A_∥(¹⁷³Yb³⁺), A_⊥(¹⁷³Yb³⁺)] for Yb³⁺ ion at the tetragonal Y³⁺ site of KY₃F₁₀ crystal are calculated from a diagonalization (of energy matrix) method. In the method, the Hamiltonian of energy matrix contains the free-ion, crystal-field interaction, Zeeman (or magnetic) interaction and hyperfine interaction terms and so a 14×14 complete energy matrix for 4f¹³ ion in tetragonal crystal-field and under an external magnetic field is constructed. Diagonalizing the energy matrix, these optical and EPR spectral data are calculated together and the calculated results are in reasonable agreement with the experimental values. The signs of hyperfine structure constants A_∥, A_⊥ for the isotopes ¹⁷¹Yb³⁺ and ¹⁷³Yb³⁺ in KY₃F₁₀ are suggested. The results are discussed.     

The study of the radiative lifetimes of 3pndF3 and 3pndD3 of Si I

The energy levels and lifetimes of 3pnd¹F₃ (n = 3-15) and 3pnd³D₃ (n = 3-18) of neutral silicon are calculated and predicted by means of the multichannel quantum defect theory (MQDT). In addition, this paper corrects the assignment mistakes of 3pnd¹F₃, 3pnd³F₃ for n > 8, and predicts many positions and lifetime values of the energy state which are not obtained in theory and experiment up to now, and analyzes the perturbation images between the channels.     

Spectroscopic and magnetic susceptibility analyses of the FJ and D4 energy levels of Tb(4f) in TbAlO3

Detailed analyses of spectroscopic and temperature-dependent magnetic susceptibility data are reported for the crystal-field split energy levels of the ⁷F_J and ⁵D₄ of Tb³⁺ in stoichiometric single crystals of ortho-aluminate TbAlO₃. The spectroscopic data include absorption spectra obtained between 2940 and 480 nm from 8 to 300 K. High resolution fluorescence spectra are reported, representing transitions from ⁵D₄ to ⁷F_6,5,4, at a sample temperature of 85 K. Using crystal-field modeling techniques recently adapted for low symmetry systems, we have assigned all 58 experimental Stark levels within the ⁷F_J and ⁵D₄ manifolds, with a fitting standard deviation of 4.5 cm⁻¹ (3.8 cm⁻¹ rms error). As a further test, the theoretical Stark levels and calculated wavefunctions were used to determine the temperature dependence of the magnetic susceptibility along the c-axis of the TbAlO₃ crystal. Good agreement is obtained between the calculated susceptibility and temperature-dependent magnetic data reported earlier, including a prediction of a 0.2 cm⁻¹ splitting of the ground-state quasi-doublet. The susceptibility calculation also confirms the predicted ordering of states within the ⁷F₆ multiplet manifold.     

Breakdown of the reduction of the rovibrational Hamiltonian: The case of SO2F2

The ground state rotational spectrum of the near-spherical top molecule S¹⁸O₂F₂ (sulfuryl fluoride) has been measured from 50 to 700 GHz. As for the parent isotopologue, S¹⁶O₂F₂ [K. Sarka, J. Demaison, L. Margulès, I. Merke, N. Heineking, H. Bürger, H. Ruland, J. Mol. Spectrosc. 200 (2000) 55-64], it was necessary to use a non-reduced Hamiltonian in order to obtain a satisfactory fit. It was possible to determine six quartic centrifugal distortion constants (instead of five for a standard asymmetric top) and five sextic constants (one of them not existing in the reduced Hamiltonian) could also be determined. This ground state level has also been analysed thanks to a tensorial formalism developed in Dijon. Only two tensorial sextic constants are fixed to zero, all others have been adjusted. Although S¹⁸O₂F₂ is less spherical than S¹⁶O₂F₂, the analysis was more difficult. It is partly due to the fact that S¹⁸O₂F₂ is oblate whereas S¹⁶O₂F₂ is prolate. The experimental quartic centrifugal distortion constants were found in good agreement with those calculated from the force field, confirming the correctness of the analysis.     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.