High-Field and Multifrequency ESR in the Two-Dimensional Triangular Lattice Antiferromagnet NiGa2S4

We report the experimental results of electron spin resonance in high magnetic fields up to about 53 T on the quasi-two-dimensional triangular lattice antiferromagnet NiGa₂S₄. The temperature dependence of the resonance field at 584.8 GHz shows a steep change below about 30 K, indicating a development of the short-range correlation. The frequency dependence of the resonance field at the lowest temperature for H∥c is explained by one of the helical resonance modes. These experimental results suggest that the short-range order is well developed at low temperatures, and the resonance mode is described by a conventional spin wave theory.     

Development of Hybrid-Type Pressure Cell for High-Pressure and High-Field ESR Measurement

A hybrid-type piston-cylinder pressure cell for the electron spin resonance (ESR) measurement has been developed. The cylinder of this pressure cell consists of a NiCrAl inner cylinder and a CuBe outer sleeve, and all inner parts are made of zirconium oxide which has good transmittance to the millimeter and submillimeter waves. We confirmed that the pressure reaches 2.1 GPa. We have also developed a transmission-type high-field ESR system having two different modulation methods for this pressure cell. A test measurement without pressure cell for the two-dimensional orthogonal-dimer spin system of SrCu₂(BO₃)₂ has been done successfully in the wide frequency region. The combination of this electromagnetic wave transmission-type pressure cell and this high-field ESR system is a promising tool for the study of the pressure-induced phase transition of SrCu₂(BO₃)₂.     

Multifrequency ESR Characterization of Paramagnetic Point Defects in Semiconducting Cubic BN Crystals

Low-frequency (X-band) electron spin resonance (ESR) investigations on commercially available large-grained cubic boron nitride (cBN) superabrasive powders of various coloration, combined with high-frequency (W-band) ESR measurements on oriented submillimeter-size single crystallites selected from the same powder samples, resulted in a clear identification of several types of paramagnetic point defects. The resulting spin Hamiltonian parameters describing the ESR spectra observed in the 3–293 K temperature range and the photosensitivity of the paramagnetic defects observed in amber-colored cBN samples are reported. It is shown that the nature of the paramagnetic centers depends on the color of the investigated samples and that, in many cases, uncontrolled impurities seem to be involved in their structure.     

Development of FEL and SASE in the far-infrared region at ISIR, Osaka University

Free electron laser (FEL) and self-amplified spontaneous emission (SASE) are being developed in the far-infrared region using the L-band electron linac at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The L-band linac was recently remodeled extensively not only for higher operational stability and reproducibility but also for high power operation of FEL. After commissioning of the linac, we first began SASE experiment with a newly-developed strong-focusing wiggler. Recently we began FEL experiment and obtained lasing with the high peak power at 70 μm again after a long break.     

Self-focusing and its related interactions at very high laser intensities for fast ignition at Osaka University

At the Institute of Laser Engineering, various type of experiments related to fast ignition were performed with the 12-beam laser system GEKKO XII and the newly added 100 TW beams line. Using both X-ray and UV laser probes, drilling via ponderomotive laser light self-focusing was studied to show drilling well into the overdense plasma over a distance of 100 μ m at a self-focused laser intensity of 10¹⁸ W / cm ² . This type of self-focusing accelerated electrons up to 0.1 to 1 MeV and was also applied to an imploding shell.     

Solvent Magnetization Artifacts in High-Field NMR Studies of Macromolecular Hydration

With the use of high magnetic fields and improved quality factor ratings of the probeheads in modern NMR spectrometers, radiation damping becomes more and more important. In addition, the demagnetizing field effect from protonated solvents gains significance with the increase of the magnetic field strength. During a typical NMR pulse sequence the magnetic fields caused by these effects become time-dependent, which makes the system nonlinear and may, for example, measurably influence the precession frequencies of all nuclei in the sample. Since radiation damping can affect signals that are several kilohertz away from the solvent resonance, the amplitude, phase, and frequency of the desired signals can be disturbed so as to give rise to spectral artifacts. In particular when difference methods are used to obtain the final spectrum, the data sets may be severely deteriorated by such artifacts. This paper investigates effects from the demagnetizing field and from radiation damping with a selection of pulse sequences in use for studies of macromolecular hydration, and strategies are described for the detection and elimination of the ensuing artifacts.     

Multifrequency Two-Dimensional Fourier Transform ESR: An X/Ku–Band Spectrometer

A two-dimensional Fourier Transform ESR (2D FT ESR) spectrometer operating at 9.25 and 17.35 GHz is described. The Ku-band bridge uses an efficient heterodyne technique wherein 9.25 GHz is the intermediate frequency. At Ku-band the sensitivity is increased by almost an order of magnitude. One may routinely collect a full 2D ELDOR spectrum in less than 20 min for a sample containing 0.5–5 nmol of nitroxide spin-probe in the slow-motional regime. Broad spectral coverage at Ku-band is obtained by use of a bridged loop-gap resonator (BLGR) and of a dielectric ring resonator (DR). It is shown that an even more uniform spectral excitation is obtained by using shorter microwave pulses of about 3 ns duration. The dead-time at Ku-band is just 30–40 ns, yielding an improved SNR in 2D ELDOR spectra of nitroxide spin-probes withT₂as short as 20–30 ns. A comparison of 2D ELDOR spectra obtained at 9.25 and 17.35 GHz for spin-labeled phospholipid probes (16PC) in 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) membrane vesicles showed that both spectra could be satisfactorily simulated using the same set of model parameters even though they are markedly different in appearance. The improved sensitivity and shorter dead-time at Ku-band made it possible to obtain orientation-dependent 2D ELDOR spectra of the Cholestane (CSL) spin-probe in macroscopically aligned lipid bilayers of egg yolk PC using samples containing only 1 mg of lipid and just 5 nmol of spin-probe.     

链接琥珀酰亚胺的线性硝酮的合成与ESR研究

该文设计并合成一种新的线性硝酮自由基捕获探针DSC-PBN(N-(4-(((2,5-dioxopy-rrolidin-1-yloxy)-carbonyloxy)methyl)benzylidene)-2-methylpropan-2-N-oxide),并采用UV、MS、1H NMR等一系列手段表征分子结构.进一步通过自由基捕获实验显示,DSC-PBN可与多种活泼自由基反应生成稳定的氮氧自由基加合物,且所得ESR谱图易于解析和分辨.由于DSC-PBN自由基捕获探针链接琥珀酰亚胺基团,可望通过与蛋白质(或多肽)N端的共价键合而应用于生物体系自由基分析.     

二茂铁基化合物的ESR研究进展

二茂铁基化合物因具有独特的氧化还原、电、光、磁和催化性能,而被广泛研究与应用.电子自旋共振(ESR)技术是观察物质顺磁性最直接的手段,在研究二茂铁基化合物的电子结构、电子转移和分子间相互作用等方面具有独特的优势.ESR技术还具有灵敏度高、样品处理简单、直接检测不破坏样品等优点.该文综述了二茂铁基化合物的ESR研究进展.     

Spin-Probe ESR Studies on Nanocomposite Polymer Electrolytes

The possibility of using spin-probe electron spin resonance (ESR) as a tool to study glass transition temperature, T _g, of polymer electrolytes is explored in 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL)-doped composite polymer electrolyte (PEG)₄₆LiClO₄ dispersed with nanoparticles of hydrotalcite. The T _g is estimated from the measured values of T _50G, the temperature at which the extrema separation 2A _zz of the broad powder spectrum decreases to 50 G. In another method, the correlation time τ_c for the spin probe dynamics was determined by computer simulation of the ESR spectra and T _g has been identified as the temperature at which τ_c begins to show temperature dependence. While both methods give values of T _g close to those obtained from differential scanning calorimetry, it is concluded that more work is required to establish spin-probe ESR as a reliable technique for the determination of T _g.     

Physics of Polymers at the Italian High-Field EPR Facility: Heterogeneities and Fast Dynamics

The reorientation of the paramagnetic molecule 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) dissolved in glassy polystyrene (PS) is studied by electron paramagnetic resonance (EPR) spectroscopy in a wide range of Larmor frequencies (9–285 GHz). High-field EPR reveals that TEMPO rotates by small angular steps with a distribution of correlation times and is able to detect the onset of fast motion of PS. Differently, X-band EPR shows that TEMPO undergoes a large-angle reorientation with virtually no distribution of correlation times and largely misses the fast dynamics of PS. A unified view is proposed. Authors' address: Dino Leporini, Dipartimento di Fisica "Enrico Fermi", Università di Pisa, Largo Pontecorvo 3, Pisa 56127, Italy     

快速电子辐照F-40和ESR和DSC研究

室温时空气中辐照F - 4 0样品中残存有链侧和链端过氧化自由基 ,这些自由基在室温下衰变缓慢 .DSC研究表明 ,F - 4 0样品熔融温度Tm 随辐照剂量的增加而下降 ,本文用聚合物片晶熔融的一般模型加以解释 .     

烯烃聚合催化剂的ESR研究进展

很多烯烃聚合催化剂都含有过渡金属离子. 由于很多过渡金属离子存在未成对电子,ESR可以检测这些含有未成对电子的过渡金属离子,所以ESR检测技术可以被用于聚烯烃催化剂的研究. 该文综述了近年来ESR技术在烯烃聚合催化剂表征领域的研究进展,根据不同过渡金属分类讨论,主要涉及了Ti、Ni、V、Cr等几种常见的过渡金属催化剂的ESR研究.     

ESR and ESR microscopy in geosciences and radiation dosimetry

ESR and its microscopic imaging (microscopy) have found new applications in interdisciplinary fields related with geosciences and with radiation dosimetry. Geological, archaeological and forensic dating has been made through paleo-dosimetry of natural radiation and chemical reactions of both radical formation and valency changes. ESR microscopy, especially the simple scanning method has a potentiality to be used in various fields. New applications of ESR are briefly reviewed with some examples.     

我国电子自旋共振波谱领域研究的50年回顾

电子自旋共振(ESR)波谱技术自1944年发现以来, 迄今已在化学、物理学、地矿学、生物学特别是生命科学的许多领域得到广泛应用, 由初期主要是对长寿命和稳定的顺磁粒子的研究, 逐步发展到对短寿命中间体, 反应过程机理和动力学的研究. 在检测技术方面, 日益广泛 地采用自旋标记, 自旋捕捉, 时间分辨ESR, 电子 核双共振, 化学诱导动态电子极化(CIDE P )和自旋回波等技术. 我国从20世纪50年代末开始将ESR技术用于某些研究领域, 80年代以后有了很快的发展. 以下仅就我国几十年来ESR研究领域的几个主要方面予以简单回顾. 有关文献引用只限于国内外核心刊物正式发表的论文和报道.