Solid state NMR characterisation of crystalline Na2OZrO2SiO2 phases

The NMR interactions of crystalline phases in the system Na₂O-ZrO₂-SiO₂ have been studied by a combination of static and magic angle spinning NMR methods for the first time. A full multinuclear (¹⁷O, ²³Na, ²⁹Si and ⁹¹Zr) approach has been employed that allows the phases to be clearly identified. NMR interactions such as ²⁹Si isotropic chemical shift correlate with the known structural units present. For ²³Na the different sites can often be distinguished on the basis of differing quadrupolar interactions.     

Excitation of ΔL = 1 resonances in the (p,n) reaction on Zr, Sn, Ce and Pb at Ep = 41 MeV

A broad peak was systematically observed at about 10 MeV above the Gamow-Teller resonance in the ⁹⁰Zr, ¹²⁰Sn, ¹⁴⁰Ce, ²⁰⁸Pb (p,n) reactions at E_p = 41 MeV. The angular distribution shapes of these peaks support the interpretation that they they correspond to ΔL = 1 state. The data are compared with TDA-DWBA calculations.     

95Zr(n,γ)96Zr的间接测量

95Zr（n,γ）96Zr是稳定燃烧的恒星中合成96Zr的唯一途径,对研究恒星演化和重元素合成具有重要的意义。由于95Zr半衰期为64 d,直接测量95Zr（n,γ）96Zr截面极为困难,因此,本工作采用替代比率法间接测量95Zr（n,γ）96Zr截面。本工作测量了94Zr（18O,16Oγ）96Zr和90Zr（18O,16Oγ）92Zr反应,得到了复合核96Zr*和90Zr*衰变到γ道的几率比,并利用截面已知的91Zr（n,γ）92Zr截面乘以实验所测比率,得到了E_n=0~8 MeV能区的95Zr（n,γ）96Zr中子俘获截面。95Zr(n, γ)96Zr cross section is important for the study of stellar evolution and heavy elements nucleosynthesis because the reaction is the only way to produce the 96Zr in Asymptotic giant branch stars. The direct measurement of 95Zr(n, γ)96Zr is very difficult due to the short half-life of 95Zr, 64 days. The surrogate ratio method was carried out to measure 95Zr(n, γ)96Zr cross sections. We measured the 94Zr(18O, 16Oγ)96Zr and 90Zr(18O, 16Oγ)92Zr reactions and obtained the γ-decay probability ratio of compound nuclei 96Zr* and 92Zr*. The 95Zr(n, γ)96Zr cross section is determined by the obtained ratio multiplying the known 91Zr(n, γ)92Zr cross section at E_n=0~8 MeV.     

29Si and 19F MAS NMR spectra of isolated 29Si(19F)2 and 29Si(19F)3 spin systems: experiments and simulations

We consider ²⁹Si and ¹⁹F MAS NMR spectra of isolated ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems in two organosilicon compounds of the type RR’SiF₂ and RSiF₃(R,R′=organic ligands). Experimental spectra are analysed by means of numerical simulations. It is found that the SiF₃ group in RSiF₃ is reorienting rapidly around the molecular Si–C bond direction in the solid state. The two ¹⁹F shielding tensors in RR’SiF₂ have strongly differing orientations relative to the two Si–F bond directions in the molecule. Possibilities and limitations of straightforward MAS NMR approaches for the full characterisation of ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems and other dipolar coupled two and three-spin systems are discussed.     

Proton–neutron structure of the N=52 nucleus Zr

Following the successful identification of mixed-symmetric one- and two-phonon states in the N=52 nuclei ⁹⁴Mo and ⁹⁶Ru, we have performed a photon scattering experiment on the N=52 isotone ⁹²Zr. Experimental data and shell model calculations show that both, single particle and collective degrees of freedom are present in the low-lying levels of ⁹²Zr. The second excited quadrupole state shows the signatures of the one-phonon mixed-symmetric 2⁺ state, while calculations and data indicate an almost pure neutron configuration for the 2⁺₁ state, in contradiction with the F-spin symmetric limit. Furthermore, two strong dipole excitations, which are candidates for the two-phonon quadrupole–octupole coupled E1 excitation and for the mixed-symmetric 1⁺ two-phonon state, were observed.     

应用多核固体核磁共振光谱与量子化学计算的方法研究层状的过渡金属硫化物

层状的过渡金属硫化物及其衍生物在许多领域内有着广泛的应用前景. 具体应用包括催化、陶瓷、润滑、能量储存、半导体、电子与光学器件. 该文报道了作者最近用固体核磁共振光谱的方法来表征几种有代表性的过渡金属硫化物(MS₂: M=Zr, Ti, W, Mo和Ta)的结果. 并在不同的磁场强度下（21.1、14.1、9.4 T）成功地获取了³³S, ^47/49Ti,⁹¹Zr,⁹5Mo 在天然丰度下的固体核磁共振光谱. 为了帮助解释实验结果,同时还进行了量子化学计算. 实验及理论计算的结果都表明³³S, ^47/49Ti, ⁹¹Zr, ⁹⁵Mo 的固体核磁共振参数对于这些核的局部几何与电子环境非常敏感.     

Rotation-vibration coupling effects in the nucleus Si

Faessler and Greiner's rotation-vibration coupling theory allows us to interprete the low-energy part of the excitation spectrum of ²⁹Si, as well as to see that the l = 2 j-effect and the non-stripping type angular distributions observed in the ²⁸Si(d,p)²⁹Si reaction are interrelated phenomena.     

Reversible H2 passivation of Si ≡ Si3 interface defects in (1 1 1)Si/SiO2

K-band electron spin resonance (ESR) at 4.3 K has revealed the dipole-dipole (DD) interaction effects between [1 1 1]P_b centers (^*Si ≡ Si₃ defects with unpaired sp³ hybrid [1 1 1]) at the 2 dimensional (1 1 1)Si/SiO₂ interface. This has been enabled by the perfectly reversible H₂ passivation of P_b, which affects the defect's spin state. Sequential hydrogenation at 253–353°C and degassing treatments in high vacuum at 743–835°C allowed to vary the P_b density in the range 5 × 10¹⁰ < [P_b] (1.14 ± 0.06) × 10¹³ cm^-2. With increasing [P_b] fine structure doublets are clearly resolved. It is found that (1 1 1)Si/SiO₂ interfaces, dry thermally grown at ≈920°C, naturally comprise a ^*Si ≡ Si₃ defect density — passivated or not — of 1.14 × 10¹³ cm^-2.     

Studies of silicophosphate derivatives by 31P-->29Si CP MAS NMR

We show that it is possible to efficiently transfer magnetization from ³¹P to ²⁹Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si₅O(PO₄)₆, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of ²⁹Si spectra from ³¹P→²⁹Si CP, enabling the studies of derivatives involving Si–O–P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates.     

丝光沸石催化剂的固体高分辨核磁共振研究

利用²⁹Si MAS NMR及²⁷Al MAS NMR技术研究了丝光沸石催化剂制备过程中的结构变化,并利用Al的四极作用大小来区分重叠在一起的不同的Al物种.     

Effects of magic-angle spinning on spin-lattice relaxations in talc

The spin-lattice relaxation times T₁ of ¹H and ²⁹Si spins in talc have been measured at room temperature with and without magic-angle spinning (MAS) of the sample. Paramagnetic impurities work as relaxation centers. ¹H T₁ depends on the spinning rate, whereas ²⁹Si T₁ is independent of the spinning rate. These facts demonstrate that spin diffusion plays an important role in ¹H relaxation but not in ²⁹Si relaxation. ²⁹Si spins relax through dipole-dipole interactions with electron spins directly, which mechanism is not affected by spinning. The relaxation rates have been analyzed theoretically.     

Si CP/MAS NMR of phosphorus-bearing organosilicon compounds

While liquid-state ²⁹Si NMR of phosphorus-bearing organosilicon compounds with more than one phosphorus per molecule can take advantage of the presence of J-coupling ⁿJ(³¹P²⁹Si) for purposes of structural assignment from J-coupling patterns, conventional ²⁹Si CP/MAS spectra of such molecular solids do not reveal structural details in a straightforward manner. For such compounds it is necessary to obtain ²⁹Si CP/MAS spectra under conditions of simultaneous ¹H- and ³¹P-high power decoupling in order to derive reliable ²⁹Si chemical shift information. ²⁹Si CP/MAS NMR spectra, obtained with and without ³¹P high power decoupling during the acquisition time, of several organosilicon compounds containing Si_xP_y (x = 1 −10, y = 1 −10) moieties are reported.     

关于93Mo中21/2+晕阱的来源(英文)

本研究通过壳模型计算研究了N=51的同中子素91Zr、93Mo和95Ru中高自旋晕态21/2+的同核异能态现象。计算发现,低角动量的p_1/2轨道上的质子是仅在93Mo中存在21/2+晕阱的主要原因。同时,本工作还研究了N=52的同中子素92Zr、94Mo和96Ru中10₁+-12₁+能级结构的系统性,发现94Mo中的10₁+-12₁+能级间隙相对最小,考虑到与93Mo的17/2₁+-21/2₁+能级相似的组态,这一结果为93Mo中出现21/2+晕阱提供了补充性的论证。Isomerism of the high-spin yrast 21/2+ states of the N=51 isotones 91Zr, 93Mo and 95Ru has been investigated using the shell model calculations. It is found that the low-j πp_1/2 is responsible for the only yrast trap in 93Mo. In addition, the relatively smaller 10₁+-12₁+ level spacing in 94Mo has been found by investigating the systematics of the 10₁+-12₁+ level structures in the N=52 isotones 92Zr, 94Mo and 96Ru. This result provides a supplementary argument to the origin of the 21/2+ yrast trap in 93Mo from the viewpoint of the similarity between the configurations of 10₁+-12₁+ states in 94Mo and those of 17/2₁+-21/2₁+ states in 93Mo.     

Single-hole-core coupling in the N = 50 region

The level schemes and electromagnetic properties of ⁸⁵Kr, ⁸⁵Sr, ⁸⁷Sr and ⁸⁹Zr are calculated in a semi-microscopic model which couples the neutron hole motion in the N = 28–50 shell to the quadrupole and octupole vibrations of the core. The calculations are compared with recent experimental results.     

Y型沸石脱铝机制和铝状态的NMR研究

对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,²⁹Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,²⁷Al MAS NMR谱、二维章动NMR及¹H-²⁷Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合²⁹Si和²⁷Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。     

Na_2~+离子较低电子态势能曲线和光谱常数的理论研究

通过多组态相互作用方法,结合原子有效芯势与极化势,利用非收缩的高斯基函数,计算了Na_2~+分子对应最低9个解离限的36个电子态的势能曲线.基于计算获得的束缚态势能曲线,拟合给出了相应的光谱常数,并与已有的实验和理论结果进行了比较.同时,给出了部分电子态的振动-转动能级和一些同类态避免交叉点的信息.计算获得的光谱信息对冷原子分子光谱与动力学的研究具有参考价值.     

One- and two-dimensional solid-state magic angle spinning NMR studies on the hydration process of layered sodium disilicate SKS-6

Three different kinds of silanols, which include isolated silanol, silanol I (with the hydroxyl proton bonded to an oxygen atom in the adjacent layer) and silanol II (with the hydroxyl proton bonded to the non-bridging oxygen at the same silicon atom), are generated during the hydration process of SKS-6 (δ-Na₂Si₂O₅). ¹H–¹H nuclear Overhauser enhancement spectroscopy reveals that the proton of silanol I has an effective chemical exchange or spin diffusion with the proton of hydrogen-bonded water, while the proton of silanol II is likely far away from the other proton-containing species. ²⁹Si magic angle spinning, ¹H→²⁹Si CP/MAS NMR and ¹H–²⁹Si phase-modulated Lee–Goldburg decoupled correlation experiments demonstrate that the local environments of the silicon sites in the final hydrated sample are mainly composed of Q² [(SiO)₂Si(OH)O⁻Na⁺], Q³ [(SiO)₃Si(OH) and (SiO)₃SiO⁻Na⁺] and Q⁴ [Si(OSi)₄] groups.     

In-band M1 and E2 transition rates and collective structures in Ba

Subpicosecond mean lifetimes of eight excited states in ¹²⁸Ba populated via the ⁹⁶Zr(³⁶S,4n) reaction were measured by the Doppler-shift attenuation (DSA) technique using a line-shape analysis. The differential decay-curve method (DDCM) was applied for the lifetime determination. The B(E2) values in the yrast band indicate that the first band-crossing is with a proton S-band. The configuration πh_11/2d_5/2 of the negative-parity semi-decoupled bands is confirmed by the measured B(E2, I → I − 2) and B(M1, I → I − 1) transition strengths. The higher-lying “dipole” band in ¹²⁸Ba can be described as a high-K four-quasiparticle band built on the prolate configuration (πh_11/2d_5/2) (νh_11/2g_7/2).     

13C及29Si核磁共振研究苯乙烯-二甲基硅氧烷嵌段共聚物的弛豫及分子运动

用¹³C及²⁹Si核磁共振研究了苯乙烯(S)及二甲基硅氧烷(Si)嵌段共聚物中硅氧烷软段的固体及溶液谱的自旋-晶格弛豫时间T₁。固态嵌段共聚物主链²⁹Si及侧甲基¹³C的T₁都与均聚物的T₁相近,但在CdCl₃溶液中各种嵌段共聚物的T₁与均聚硅氧烷相差颇大。用偶极-偶极相互作用来解释高聚物的自旋-晶格弛豫。苯乙烯-二甲基硅氧烷嵌段共聚物具两相结构,所以嵌段共聚物中软段及硬段微区中链段的运动与在均聚物分子中链段的运动模式基本相同。而CdCl₃对聚苯乙烯或聚硅氧烷都是良溶剂,软段硬段之间有相互影响。所以其链段运动与均聚物不同,从而导致链段运动的相关时间τ_c变短和T₁的增长。     

采用相对论多组态Dirac-Hartree-Fock方法对Mg原子同位素位移的理论研究

利用相对论多组态Dirac-Hartree-Fock方法研究了Mg原子基态到低激发态~1S_0-~1P_1和~1S_0-~3P_1两条跃迁谱线的同位素位移参数,包括正常质量位移系数,特殊质量位移系数和场位移因子,并计算了~(24)Mg,~(25)Mg和~(26)Mg三个稳定同位素的同位素位移.在计算中采用了一种受限制的双电子激发模式,并将同位素位移计算结果与已有的实验测量和理论计算结果进行了对比.结果表明,用本文的研究方法计算的Mg原子同位素位移与其他理论结果和实验测量值十分符合.本文的计算结果可以为~(20-40)Mg同位素位移测量实验提供必要的参考,所用的计算方法也可以应用到其他类Mg体系(核外电子数等于12的离子)等多电子离子的光谱结构计算和同位素位移的研究中.