BaCl_2微晶中色心的ESR谱分析

用电子自旋共振(ESR)方法研究γ(或X)射线辐照发光基质材料BaCl_2中的点缺陷发现,在室温下有三个ESR峰。根据ESR信号朗德因子g值,信号强度受热衰减和时间衰减特征分析,确认这三个峰分别为BaCl_2微晶中的三种色心:V_K心、H心和F心。     

BaF2中Vk心的ESR谱分析

电子自旋共振（ＥＳＲ）实验间接表明，γ射线辐照能在室温下在ＢａＦ２微晶中产生Ｆｒｅｎｋｅｌ激子这样的元激发，此元激发受热在１５０℃以下消失。γ射线辐照使ＢａＦ２微晶中Ｆ－离子上的２Ｐ电子跃迁到外层轨道，并与２Ｐ轨道的空穴形成紧束缚的电子－空穴对——Ｆｒｅｎｋｅｌ激子。激子中的电子受热脱离Ｆ原子，这种晶格上的Ｆ０是ＥＳＲ可探测的顺磁色心点缺陷——Ｖｋ心。受γ射线辐照的ＢａＦ２微晶中含有Ｆｒｅｎｋｅｌ激子，受热时Ｆｒｅｎｋｅｌ激子湮灭。Ｖｋ心增多的现象，表现为随温度增高Ｖｋ心的ＥＳＲ信号增强的反常现象。     

Gd5Si1.75Ge1.75Sn0.5的结构、磁相变与磁熵变

采用粉末XRD和振动样品磁强计研究了Gd5Si1.75Ge1.75Sn0.5合金的结构、磁相变和低场变化下的磁熵变。磁性测量结果表明,Gd5Si1.75Ge1.75Sn0.5合金的磁化强度在居里温度附近发生突变,具有一级相变的典型特征,室温具有Gd5Si2Ge2型单斜结构;合金低场磁热效应非常明显,1.8T磁场变化下,在其居里温度272K附近的最大磁熵变为16.7J.kg-1.K-1。用成本低廉的Sn取代Gd5Si2Ge2中部分Si和Ge后,Gd5Si1.75Ge1.75Sn0.5在低磁场变化下的磁熵变比金属Gd大得多并略高于Gd5Si2Ge2。     

D-和L-丙氨酸的磁手性相变

利用变温直流磁化率测定, 在外加磁场强度为1 T, 磁场平行晶体c轴, 发现在温度270 K, D-和L-丙氨酸发生磁手性相变. 结合中子衍射确定磁手性相变机制为, D-和L-丙氨酸中的(N+H)有类金属氢原子特性, 在相变点270 K, 由(N+H)释放的电子自旋有磁手性. 用变温偏振拉曼光谱进一步证明, D-丙氨酸中的(N+H)的电子自旋(↑), 而L-丙氨酸中的电子自旋(↓), 处于高低不同的能态.磁手性相变(宇称和时间反演都破缺)能差为10^-4-10^-5 eV·molecule^-1.     

电感耦合等离子体质谱法测定高纯铁中21种元素时的基体效应北大核心CSCD

对用电感耦合等离子体质谱法测定纯铁中21种元素(包括Li、Be、B、Al、Ti、Mn、Co、Ni、Cu、Zn等),通过加入高纯铁作为基体,试验考察了不同量的铁基体对上述被测元素的信号强度的影响。结果发现:铁基体质量浓度在40mg·L^(-1)以内时,待测元素的相对信号强度与铁基体浓度保持较好的线性关系;当铁基体质量浓度增大至400mg·L^(-1)时,除了Mn、Co两元素外,铁基体对其他待测元素均产生一定的抑制作用。基于对内标元素的基体效应分析,选择与待测元素有相似基体效应的内标元素,以校正基体效应。     

新型水溶性硫杂蒽酮类光引发剂的光化学性能研究

本文对8种水溶性硫杂蒽酮类光引发剂进行了紫外 可见光谱、荧光光谱以及电子自旋共振光谱(ESR)等测试。测定了最大吸收波长,计算了摩尔消光系数,荧光量子产率,测定了ESR信号强度等。并对其结构与光化学性能之间的关系进行了讨论。     

ErFe_(11)Ti化合物在流动氮气氛中的差热-热重分析

通过X射线衍射(XRD)、差热-热重(DTA-TG)联用仪以及磁测量等手段研究了ErFe11Ti化合物在流动氮气氛从室温(~300 K)到1473 K升温过程中成分、结构及居里温度等变化行为。结果表明,温度为600 K左右时,ErFe11Ti化合物吸氮反应最剧烈,吸氮以后化合物的居里温度TC有明显提高。当温度较高时,ErFe11Ti可能部分分解为Er-N,α-Fe(Ti)。α-Fe和Ti分别在860和1300 K左右发生吸氮反应,生成FeNy和Ti2N2。在整个升温过程中,DTA曲线未因样品升温至某成分的居里点发生而出现明显放热峰,这可能是因为样品的相变潜热较小所引起的。     

内敏乳剂的ESR研究

本文制备了具有化学结构缺陷以及具有物理晶格缺陷的两种内敏核壳乳剂,并研究了它们的电子自旋共振波谱。随着化学增感时间的增加,ESR信号强度增强,达到一最大值后又下降。ESR信号强度随核壳比的下降而下降;随灰化程度的上升而下降。不同减感染料由于其减感机理的不同,对内部感光性能和ESR信号强度的影响也不同。上述结果可以用空穴在颗粒内部的行为来解释。     

电感耦合等离子体质谱法测定高纯铁中21种元素时的基体效应

对用电感耦合等离子体质谱法测定纯铁中21种元素(包括Li、Be、B、Al、Ti、Mn、Co、Ni、Cu、Zn等),通过加入高纯铁作为基体,试验考察了不同量的铁基体对上述被测元素的信号强度的影响。结果发现:铁基体质量浓度在40mg·L~(-1)以内时,待测元素的相对信号强度与铁基体浓度保持较好的线性关系;当铁基体质量浓度增大至400mg·L~(-1)时,除了Mn、Co两元素外,铁基体对其他待测元素均产生一定的抑制作用。基于对内标元素的基体效应分析,选择与待测元素有相似基体效应的内标元素,以校正基体效应。     

多铁性铬氧化物YCrO3体系的磁特性及比热研究

系统研究了低温条件下铬氧化物YCrO3体系的磁特性及比热特点.实验结果表明,在高温区(T＞140 K)直流磁化率随温度的变化遵从居里-外斯定律,YCrO3体系处于顺磁状态,样品的有效平均磁矩μefr=3.99μB、顺磁居里-外斯温度TCw =-340 K,即体系具有反铁磁性.在TN =140 K附近,YCrO3体系经历了由顺磁态向倾角反铁磁态的相转变,其自旋磁结构一直保持为Г4(Gx,Ay,Fz;FRz);低温条件下(T＜140 K),体系具有完整闭合的磁滞回线,表明YCrO3样品具有反铁磁性的同时,具有明显的弱铁磁性,且随温度的降低铁磁性逐渐增强.对应于磁相变温度TN,比热曲线在140 K附近出现尖锐的λ形反常突起,由于Y离子没有磁性,显示了Cr3+磁矩亚晶格的顺磁-反铁磁相变对比热的贡献.     

Electron spin resonance study on homogeneous catalysts derived from n-butyl titanate and triethylaluminum

ESR spectra of homogeneous catalyst systems derived from n-butyl titanate and triethylaluminum at Al/Ti molar ratios of 1.0–10 were observed in toluene solution at several temperatures from ?78°C to +25°C. In the whole range of Al/Ti molar ratios, a single signal with a g value of 1.951 was observed at ?78°C and was associated with the first reaction intermediate. With increasing temperature, the intensity of the signal decreased gradually, while two series of signals appeared, depending on the Al/Ti molar ratio. At an Al/Ti molar ratio of 1.7, seven kinds of signals with g values of 1.960, 1.946, 1.950, 1.959, 1.980, 1.977, and 1.978, respectively, were observed. On the other hand, four kinds of signals with g values of 1.934, 1.966, 1.952, and 1.979, respectively, were found at Al/Ti molar ratios larger than 3. The structures of the species corresponding to the signals were discussed on the basis of the ESR spectra, the order of their growth and their hyperfine structures being considered. Two series of ESR signal were correlated to two kinds of active species for polymerization of styrene and butadiene, respectively.     

氧化锌纳米微晶的顺磁共振特性

半导体纳米微粒是制备新一代电子器件的理想材料［1，2］．电子自旋共振谱（ESR）是研究纳米微晶表面电子自旋构象和表面结构的一种有效方法．体相ZnO是一种抗磁性物质，通常观察不到顺磁共振信号（ESR）．有关ZnO纳米微晶电子顺磁共振特性研究还未见文献报导．本文ZnO纳米微晶是用微乳法制备的：这样就制成了纳米尺度的具有表面包覆的ZnO微粒有机溶胶．这里表面活性剂起着“空间位阻”作用，一方面防止成胶过程中粒子间的聚合，使胶粒均匀细小；另一方面，包覆能减少微粒表面缺陷，使粒子性质变得十分稳定．将上述制得的ZnO纳米微粒…     

A study of the mechanism of radiation-induced polymerization of carbon suboxide

The γ radiolysis of solid C₃O₂ at 77 K produces paramagnetic centers of several types. The ESR spectrum constitutes a number of narrow lines with an anisotropic g factor. Some of the centers are photounstable and are lost after optical bleaching. Heating the sample results initially in the loss of photounstable centers and then, in the temperature region in which solid C₃O₂ undergoes a phase transition (140 K), loss of the centers responsible for the center section of the ESR spectrum. In the temperature region 140–270 K concentration of the centers remained at the level of 10¹⁵?10¹⁶ g^?1. At higher temperatures an intense polymerization of liquid C₃O₂ followed by a sharp increase in concentration of the paramagnetic centers was observed. It is assumed that in radiolysis at 77 K and on subsequent heating the formation of oligomeric centers in solid C₃O₂ results in a decreasing probability of their loss. Using a calorimetric technique, we studied the kinetics of the postradiation polymerization of C₃O₂. Small additions of acetone (cationic inhibitor) brought about the loss of the oligomeric centers and suppressed completely all postpolymerization. The polymerization rate increased with the concentration of the resulting polymer. An autocatalytic character of the process is supposed to be connected with the formation of polymer-monomer complexes.     

ESR study of the diacetylene polymer 4BCMU

Electron Spin Resonance (ESR) measurements of the polydiacetylene 4BCMU in the solid-state indicate the presence of a thermally activated paramagnetic center with g ≈ 2.002 and first-derivative peak-to-peak linewidth of ≈ 17G. An abrupt and irreversible decrease in ESR signal intensity is observed at ca. 400 K, and appears to be associated with the solid-state planar-nonplanar conformational transformation manifested by an irreversible color change from metallic brown to red.     

Electron spin resonance study on polymerization of alkyl acrylates with n-butyl titanate(IV)–triethylaluminum catalyst

n-Butyl titanate(IV)–triethylaluminum catalyst at Al/Ti molar ratios greater than 6 polymerizes methyl and n-butyl acrylates at ?78°C. The polymerization system which includes methyl acrylate at ?78°C, gives two ESR signals with g factors of 1.958 and 1.961 that overlap each other. The absorption intensity of the latter signal is approximately proportional to the polymer chain concentration calculated from polymer yield and the molecular weight. The polymerization system at Al/Ti ratios smaller than 3 has no catalytic activity on the polymerization and shows only the ESR signal with the g factor of 1.958. On the basis of these facts the ESR signal with the g factor of 1.961 is attributed to the active growing end of poly(methyl acrylate) with this catalyst. The character of this active growing end is discussed.     

石英玻璃中顺磁缺陷中心的ESR成像

用ESR成像方法探测了石英玻璃杜瓦受紫外光辐照后产生的局部晶格缺陷——F心的空间分布情况.从F心的有梯度场ESR谱和二维ESR图象可以看出,石英杜瓦中产生的F心空间分布是不均匀的,其浓度与辐照方向和辐照强度密切相关.从F心ESR散点图计算出的石英杜瓦横截面几何尺寸与实物基本相符.     

Poly(carbon suboxide): A photosensitive paramagnetic ladder polymer

Carbon suboxide was found to give, on photo- and thermal-polymerization, a photosensitive paramagnetic polymer. Studies of the kinetics of the ESR signal growth accompanying the polymerization process complement documented results obtained from monitoring the rate of polymer production and monomer disappearance. The spin concentration of the polymer increases with higher reaction temperature, reaching 2 × 10¹⁹ spin/g at a polymerization temperature of 105°C. The paramagnetism of poly(carbon suboxide) follows the Curie—Weiss law. Relaxation behavior at room temperature and g values for the spin systems have been obtained. The 105°C polymer shows a Weiss constant equal to 17°K and an extremely narrow ESR line width, ca. 10 mG, at 5°K. The ¹³C coupling constant from the selectively labeled polymer indicates π-electron delocalization over the ladder polymer. The polymer paramagnetism can be further reversibly enhanced by visible light irradiation. The steady-state concentration of the photo-ESR signal is proportional to the square root of incident light intensity, with a quantum yield at room temperature for charge accumulation equal to 5% at an incident light level of 10¹⁵ photons/sec-cm². Fluorescence and excitation spectra of the soluble fraction of poly(carbon suboxide) are presented together with the quantum yield. The polymer has also been found to be an effective photopolymerization initiator at wavelengths longer than 340 nm.     

Electron spin resonance study of polymerization of butadiene with tris(acetylacetonato)titanium and triethylaluminum

ESR spectra of homogeneous catalyst derived from tris(acetylacetonato)titanium(III) and triethylaluminum were observed at several temperatures from ?78°C, to +25°C, at molar ratios of aluminum to titanium of 1–108. At ?78°C, this catalyst yields a violet complex which shows an ESR signal with a g value of 1.959 and is associated with the first intermediate. At ?40°C to ?30°C, this signal decreases, and two signals with g values of 1.947 and 1.960 are observed. The latter two signals diminish at ?5°C to +10°C, while two kinds of new signals with g values of 1.965 and 1.969 appear overlapping each other. The structures of the species corresponding to these five signals are discussed on the basis of the ESR spectra, the intensity change, and the unpaired spin distribution. A new signal with a g value of 1.978 is found in the presence of butadiene at 25°C at Al/Ti > 8 and is assigned to a growing end of polybutadiene with this catalyst. The polymer yield increases remarkedly at Al/Ti molar ratios greater than 10. The microstructure of the resulting polymer consists almost completely of 1,2 units. The structure of the growing end is proposed to be a titanium (III) species containing two 1-substituted allyl groups, by comparison with the structure ascribed to the growing end of polybutadiene with n-butyl titanate-triethylaluminum catalyst.     

Paramagnetic centers by X-ray-irradiation of aluminium hydroxide

EPR spectra of paramagnetic centers originating from X-ray-irradiation of aluminium hydroxide at room temperature have been measured. The EPR spectrum represents a superposition of EPR spectra of ionic centers O^–, holes of type and trapped electrons. Radiation chemical yield of paramagnetic centers observed at room temperature (293 K) is G(spins.)=4.4±0.6) spins per 100 eV absorbed energy. The decay of paramagnetic centers in irradiated Al(OH)₃ was oberved at 293 K. The rate constant of the paramagnetic centers decay in irradiated Al(OH)₃ is K₂=(0.0980±0.0019) kg·mol^–1·min^–1 and their half-life is 9.43±0.18 days.Dedicated to the memory of the late Genrikh Markovis Kolyiari.     

The polymerization of ethylene with a soluble titanium-aluminium complex

The reaction between biscyclopentadienyl titanium dichloride and aluminium alkyls and alkyl chlorides has been examined by ESR spectroscopy, and by the abilities of the various resulting complexes to initiate the polymerization of ethylene at 1 atm and ambient temperature. In general, it is concluded that the active initiating species is a Ti(IV) complex, and not the paramagnetic Ti(III) complexes. Accordingly, the development of an ESR spectrum is accompanied by a fall off in initiating efficiency, decrease in polymerization rate and increased molecular weight of the polymers produced. The reduction of Ti(IV) to Ti(III) during the polymerization accounts for the fall in rate with conversion; addition of an oxidizing agent (1:2-dichloroethane) to the polymerization converts Ti(III) to Ti(IV), as observed by the disappearance of the ESR signal, and increases the efficiency of the polymerization. Block copolymers of ethylene with propylene and butadiene have been prepared with this initiator; the efficiency in producing blocks has been used to study the decomposition of the active sites by a first order reduction process.