126Ce的EC/β＋衰变

利用187 MeV的40Ca离子轰击同位素靶92Mo,由熔合蒸发反应生成目标核126Ce。藉助氦喷嘴快速带传输系统和X-X-t与X-γ-t符合测量,首次建立了126Ce的EC/β＋衰变纲图。建议了可能属于126Ce一个高自旋同核异能态的衰变,其β衰变后布居在与126La的高自旋同核异能态相关的低位能级区,测定的半衰期是57（9）s。也建议了可能属于126Ce基态的衰变,其β衰变后布居在与126La的低自旋同核异能态相关的低位能级区,它的半衰期被测定为12（4）s。但偶-偶核126Ce存在高自旋同核异能态的物理原因还有待进一步探究。     

强偶合体系异核二维相关NMR谱解析

本文对异核二维相关NMR谱中强偶合的影响进行了分析,给出量子力学的定量描述。用所建立的计算机NMR谱解析系统模拟了AB(X)自旋体系以及蔗糖的异核二维相关谱。     

核磁共振波谱的自旋去偶技术及其在化学结构研究上的应用

核磁共振波谱在研究化学结构中占有重要的地位。在高分辨的核磁共振波谱中,磁性核之间的自旋-自旋偶合作用往往会使谱线复杂化。一方面,可以利用自旋-自旋偶合作用来确定一些化合物的结构;另一方面,由于谱线的复杂化,使得分析复杂化合物的核磁共振谱发生困难。借助于自旋去偶技术可以解决核磁共振中很多疑难问题,使核磁共振的研究工作更深入一步。因此,它是核磁共振波谱学发展中的一门重要的研究技术。必须区别两种不同的自旋-自旋偶合情况,即同一类核之间的自旋-自旋偶合(例如质子之间的偶合)和不同类核之间的偶合(例如质子同     

C—H键核自旋耦合常数和伸缩频率的自然杂化轨道研究

利用PM3级别上的最大重迭对称性分子轨道法和自然杂化轨道方法,计算了系列碳氢化合物的杂化轨道,拟合出了计算C—H键核自旋耦合常数和伸缩频率的简单关系式.研究了系列碳氢化合物中不同的C—H键核自旋耦合常数和伸缩频率.结果表明,碳氢化合物中的C—H核自旋耦合常数和伸缩频率主要取决于C原子的轨道杂化作用,为从简单价键理论角度解释和计算1JCH和νCH提供了一种简便直观的方法.     

核极化效应(NOE)及其在有机结构研究中的应用

一、引言核磁共振谱是有机结构研究中的一种常规的有力武器。近年来,核磁共振谱学又有了不少发展,核极化效应(Nuclear Overhauser Effect,简称NOE)就是其中之一。 1953年,Overhauser报告了在金属中,当电子的自旋共振被饱和时,原子核产生动态极化。 1955年,Solomon首先把这个效应用于含有核自旋的系统中,他研究了HF中的化学交换,因为是在核与核之间进行的极化效应,所以称为核极化效应。 1965年,Kaiser第一个报告质子与质子     

Dendr.PE-PAA在水溶液中自聚集的NMR研究

用1H NMR自扩散系数,核弛豫和二维NOESY谱研究了新合成苄醚树枝体与丙烯酸杂化嵌段共聚物在水溶液中生成胶团的动态行为.体系中苄醚树枝体与丙烯酸杂化嵌段共聚物的各1H核的自旋-晶格弛豫时间（T1）、自旋-自旋弛豫时间（T2）、自扩散系数和二维NOESY中的交叉峰证明苄醚树枝体与丙烯酸杂化嵌段共聚物在水溶液中形成自聚集,且与不同浓度下聚集体有差别.     

固体核磁共振弛豫在高分子研究中的应用

本文综述了近年来固体核磁弛豫方法在高分子研究中的应用，共分５个部分加以介绍：（１）自旋－晶格弛豫过程；（２）在旋转坐标系中的＾１３Ｃ自旋－晶格弛豫过程；（３）交叉极化速率和旋转坐标系中的＾１Ｈ自旋－晶格弛豫过程；（４）自旋－自旋弛豫过程；（５）动态结构导致的线形变化。本文主要讨论磁性核的各种弛豫过程以及它们与分子结构和分子运动的关系。     

稀土单分子磁体的研究进展

在信息存储和量子计算方面具有广阔应用前景的单分子磁体及相关研究中,应用各向异性显著的稀土离子以期提高单分子磁体自旋翻转能垒的研究倍受关注。 本文综述了稀土单分子磁体的研究进展,并着重介绍了单核、三核及四核镝配合物单分子磁体的磁学性质。     

用2D NOESY和1H NMR弛豫研究月桂醇聚氧乙烯(23)醚(Brij-35)胶团的结构状态

浓度为100倍临界胶团浓度(cmc)的月桂醇聚氧乙烯(23)醚的¹H NMR自旋-晶格弛豫时间、自旋-自旋弛豫时间和核-核Overhauser效应谱表明,处于胶团核外面的亲水聚氧乙烯链呈卷曲收缩状均匀地堆积在胶团核的表面,在结构上形成了一个包含一定量水分子的厚而疏松的亲水网络层.亲水网络层是和溶剂(即水)相溶合的,这样可以作为一个过渡层保持胶团溶液的稳定.¹H NMR弛豫时间表明亲水聚氧乙烯链的运动和疏水烷基链的运动一样,都是受阻的.2D NOESY实验所观察到的胶团核外亲水链和它内部的疏水链质子间的相互作用,直接证明了Brij-35胶团亲水部分和疏水部分质子间距很短.     

聚合物异核交叉弛豫及二维NOE谱

Kover和Batta首次采用选择性质子π脉冲来测定~(13)C自旋-晶格弛豫速率并与常规反转回复法测定的自旋-晶格弛豫速率相比较求出了交叉弛豫速率,并以此来计算异核间的距离,但他们的计算方法仅适用于满足极端窄化条件的刚性球状分子。二维异核NOE谱(HOESY)是1983年才发展起来的二维NMR技术,它可用来研究异核间的交叉弛豫作用及研究分子间相互作用。Kover和Batta在此方面作了许多     

Spin selective multiple quantum NMR for spectral simplification, determination of relative signs, and magnitudes of scalar couplings by spin state selection

In the present work we demonstrate a novel method for spectral simplification and determination of the relative signs of the scalar couplings using a spin selective multiple quantum NMR experiment. A spin selective excitation of double quantum coherence of A and M spins in a weakly coupled three spin system of the type AMX, results in a doublet in the double quantum dimension whose separation corresponds to the sum of couplings of the active spins to the passive spin X. One component of the doublet has the passive spin X in mid R:alpha state while the other component has the passive spin X in mid R:beta state. The spin selective conversion of double quantum coherence to single quantum coherence does not disturb the spin states of the passive spin thereby providing the spin state selection. There will be two domains of single quantum transitions in single quantum dimension at the chemical shift positions of A and M spins. The mid R:alpha domain of A spin is a doublet because of mid R:alpha and mid R:beta states of M spin only, while that of mid R:beta domain is another doublet in a different cross section of the spectra. The scalar coupling J(AM) can be extracted from any of the mid R:alpha and mid R:beta domain transitions while the relative displacements of the two doublets between the two domains at the two chemical shifts provides the magnitude and sign of the scalar coupling J(AX) relative to the coupling J(MX). Similar result is obtained for zero quantum studies on AMX spin system. The proposed technique is discussed theoretically using product operator approach. The new spin state selective double quantum J-resolved sequence has also been developed. The methodology is confirmed experimentally on a homonuclear weakly coupled three spin system and applied to two different heteronuclear five spin systems.     

氢核磁共振谱自旋耦合裂分现象的量子力学解释

Hydrogen nuclear magnetic resonance spectroscopy (¹H-NMR) is an important content in the university course of instrumental analysis and organic structure analysis. The splitting law of spin coupling between hydrogen nuclei is the focus of teaching and learning. Most textbooks explain that the cause of spin coupling splitting is due to the local magnetic field produced by the different spin orientation of other adjacent nuclei (nuclei magnetic dipole-dipole interaction, direct nuclear spin coupling), and a few monograph on Nuclear Magnetic Resonance refers to electron spin polarization mediated nuclear spin coupling (indirect nuclear spin coupling). Here we introduce quantum mechanics for explanation of the splitting law of spin coupling between hydrogen nuclei.     

Mechanism and origin of exciton spin relaxation in CdSe nanorods

The dynamics of exciton spin relaxation in CdSe nanorods of various sizes and shapes are measured by an ultrafast transient polarization grating technique. The measurement of the third-order transient grating (3-TG) signal utilizing linear cross-polarized pump pulses enables us to monitor the history of spin relaxation among the bright exciton states with a total angular momentum of F = +/-1. From the measured exciton spin relaxation dynamics, it is found that the effective mechanism of exciton spin relaxation is sensitive to the size of the nanorod. Most of the measured cross-polarized 3-TG signals show single-exponential spin relaxation dynamics, while biexponential spin relaxation dynamics are observed in the nanorod of the largest diameter. This analysis suggests that a direct exciton spin flip process between the bright exciton states with F = +/-1 is the dominant spin relaxation mechanism in small nanocrystals, and an indirect spin flip via the dark states with F = +/-2 contributes as the size of the nanocrystal increases. This idea is examined by simulations of 3-TG signals with a kinetic model for exciton spin relaxation considering the states in the exciton fine structure. Also, it is revealed that the rate of exciton spin relaxation has a strong correlation with the diameter, d, of the nanorod, scaled by the power law of 1/d4, rather than other shape parameters such as length, volume, or aspect ratio.     

Effect of rapidly relaxed electron spin anisotropically coupled to nearby nuclear partners

In practice, many situations arise when a perturbed nuclear spin relies upon the aid of a rapidly relaxed spin neighbor in order to realize thermal equilibrium. Conventional treatments view the efficiently relaxed spin as part of the 'lattice', invoke the secular approximation, and consider the associated time correlation of the lattice variables, phenomenologically. Recently, an ab initio perturbative approach has been proposed for investigation of these spin systems. In this work, a similar formalism is applied to the scenario, in which nuclear spin relaxation is effected via an anisotropically coupled, efficiently relaxed, spin. Interesting conflicts with standard theory are revealed. Furthermore, although left mostly unexplored, this approach lends insight into numerous related aspects of magnetic relaxation including separation of timescales, distinction between spin and spatial averaging, paramagnetic relaxation, Curie spin relaxation, and the dynamic frequency shift.     

Investigation of the incommensurate and commensurate magnetic superstructures of LiCuVO4 and CuO on the basis of the isotropic spin exchange and classical spin approximations

The spin lattices of magnetic oxides LiCuVO(4) and CuO are made up of CuO(2) ribbon chains. The incommensurate and commensurate magnetic superstructures of these oxides were examined by calculating the total spin exchange interaction energies of their long-range order spin arrangements on the basis of the isotropic spin exchange and classical spin approximations. The incommensurate superstructure (0, 0.532, 0) of LiCuVO(4) was analyzed to find that the next-nearest-neighbor spin exchange interaction J(nnn) is more strongly antiferromagnetic than the nearest-neighbor spin exchange interaction J(nn) in the CuO(2) chains. With this finding, we reassessed the relative strengths of the spin exchange interactions of LiCuVO(4) and CuO and then analyzed the relative energies of their long-range order spin arrangements. The incommensurate superstructure (0, 0.532, 0) of LiCuVO(4) is explained when the J(nn)/J(nnn) ratio is -0.40. Both the incommensurate superstructure (0.506, 0, -0.483) and the commensurate superstructure (0.5, 0, -0.5) of CuO, which occur at 231 and 212.5 K, respectively, are well explained in terms of the calculated total spin exchange interaction energies. The incommensurate superstructure of CuO becomes commensurate by a slight change in one interchain spin exchange interaction, which is due probably to a slight structure change brought about by the temperature lowering.     

Exploring two-state reactivity pathways in the cycloaddition reactions of triplet methylene

Spin forbidden 1,2-cycloadditions of triplet methylene to alkenes have been theoretically studied as an example of the two-state reactivity paradigm in organic chemistry. The cycloadditions of triplet methylene to ethylene and the (E)- and (Z)-2-butene isomers show spin inversion after the transition state and therefore with no effect on the reaction rate. A local analysis shows that while triplet methylene addition to alkenes leading to the formation of a biradical intermediate is driven by spin polarization, the ring closure step to yield cyclopropane is a pericyclic process. We have found that at the regions in the potential energy surface where the spin crossover is likely to occur, the spin potential in the direction of increasing spin multiplicity, mu(+)(s), tends to equalize the one in the direction of decreasing spin multiplicity, mu(-)(s). This equalization facilitates the spin transfer process driven by changes in the spin density of the system.     

Analysis of the spin exchange interactions in the three phases of vanadium pyrophosphate, (VO)2P2O7, in terms of spin-orbital interaction energy

The spin exchange interactions in the ambient-pressure orthorhombic (APO), high-pressure orthorhombic (HPO), and ambient-pressure monoclinic (APM) phases of the vanadium pyrophosphate, (VO)2P2O7, were analyzed by calculating the spin-orbital interaction energies delta e-delta e0 of their spin dimers. The anisotropy of the spin exchange interactions in the HPO phase is well explained by the delta e-delta e0 values. For the APO phase, the reported crystal structure does not provide accurate enough delta e-delta e0 values to conclude unambiguously which of the V1-V2 and V3-V4 chains has a larger spin gap and which of the bridged and edge-sharing spin dimers has a stronger spin exchange interaction in the V1-V2 and V3-V4 chains. The APM phase is predicted to exhibit essentially two spin gaps, with a large spin gap for the V8-V5-V7-V6 chain and a very small one for the V4-V2-V3-V1 chain.