选择照射下核自旋波函数的变换特性

本文采取适用于一般多量子跃迁过程的讨论方法,当任意自旋的核处于恒定磁场和静电场中并受到单频或多频选择照射的条件下,对单个核的任意数目的相邻的子能级系统,其几率振幅的变换特性作一普遍分析,同时还讨论了上述变换特性的物理含义,阐明了粒子在空间旋转变换下波函数的2π或4π对称性,以及粒子在选择照射下子能级系统的几率振幅的2π或4π周期性的区别。 关键词：     

魔角的准确快速确定

慢旋转条件下,四极相互作用产生的FID分解为一系列旋转回波。当旋转轴向与外磁场方向夹角趋近于魔角时,观测到的回波数增加。由此,可在MAS-NMR实验中准确、迅速地确定魔角。本文分析了自旋为1的核的FID解析式,理论上解释了这一现象。以氘代HMB为例的实验证明确定魔角的准确度可达到±0.05°的数量级。 关键词：     

镜煤及其吡啶不溶物与可溶物的固态NMR研究

本文对镜煤及其吡啶可溶物与不溶物进行了¹³C CPMAS及¹H CRAMPS NMR研究,获得了煤的12种结构参数,并估算了芳环簇的大小.结果表明:镜煤吡啶可溶物芳环簇结构尺寸较小,平均为2—3个环,脂构碳含量较高;而不溶物芳环簇结构尺寸较大,平均为5个环,脂构碳含量较低.样品中顺磁离子浓度是影响¹H和¹³C自旋晶格弛豫时间的重要因素.由弛豫时间的测量分析可知,吡啶的抽提过程有效地带走了样品中的顺磁中心,抽提后的产物即吡啶不溶物与可溶物的自由基浓度都降低了,而可溶物的自由基浓度降低更为显著.     

利用Raman磁共振研究四极核对AX体系弛豫行为的影响

本文利用一维多量子Raman磁共振谱线的线宽测定了氯仿(CHCl₃)中碳氢体系的多量子的弛豫时间,由此得到第二类标量耦合弛豫起主导作用时的碳氢核自旋弛豫的交叉相关系数,氯核与碳和氢核的标量耦合常数,以及它们的相对符号。     

NMR波谱学中的高温近似的有效性及其相关问题

高温近似(HTA)是NMR波谱学和MRI技术中久经考虑且应用最广的一个近似. 最近几年有一大批引人注目的文章断言对高场下的浓溶液，如水的质子COSY谱，该近似会 失效. 与声称的HTA失效同样令人惊讶的是其副产品之一，即认为在低粘度液体如水里，存 在分子间的多量子相干(MQC). 根据理论分析及实验结果，本文将对液体中HTA和分子间MQC 作一仔细考查. 结论是：(1)室温下，常规NMR样品如水，不是一个宏观量子系统；(2)室温下，HTA仍然是NMR里最值得信赖的近似；(3)质子COSY谱(如水)中所观察到的多重自旋回波( MSE)峰并不意味存在分子间的量子力学自旋相互作用.     

AX体系多量子弛豫时间的直接探测

本文建议了一种直接测量AX系统多量子弛豫的方法。不用作两维谱,测量过程类似于常规弛豫时间测量,实验简便、准确。由所测得的单量子和多量子弛豫时间可以导出起伏场的交叉相关系数,这提供了单量子NMR所不能获得的信息。本文还讨论了AX体系多量子弛豫机理的特殊性。 关键词：     

低磁场条件下天然气核磁共振特性的实验研究

研究天然气在低磁场条件下的核磁共振弛豫特性及含烃因子的变化对天然气的勘探和开发工作具有重要意义,由于受核磁共振仪器耐温、耐压条件的限制,这方面的研究工作非常少,国内还是空白. 本文在一套自行研制的耐高温、耐高压的低磁场(磁场强度0.056T )核磁共振设备上,对我国大庆油田深层天然气的核磁共振特性进行了实验研究,获得了天然气的T₁弛豫时间、含烃因子随温度和压力变化的函数关系. 本文的研究内容对我国正在开展的核磁共振测井工作具有重要的参考价值.     

用23Na和27Al固体核磁共振研究Na+在γ-Al2O3上的吸附状态

The adsorption of Na~+ on γ-alumina surface at four coverages of Na_2CO_3 (5%, 10%, 15%, and 20% wt/wt) was characterized by solid-state ~(23)Na and ~(27)Al NMR spectroscopy. The experimental results suggest that two distinct adsorbed species are present on alumina surface: surface species and surface salts. At lower coverages of Na_2CO_3 (5% and 10%), a surface species is predominant, in which the Na~+ cations are associated with the oxygen atoms of γ-alumina. With increasing the loading level to 15%, a second adsorbed species begins to appear which is attributed to the surface salt, Na_2CO_3, deposited on the solid surface. Further adsorption of Na_2CO_3 leads to an increase in the amount of surface salt while the amount of surface species remains unchanged. ~1H-~(27)Al CP/MAS experiments give the evidence that some Na~+ cations in the form of surface species are coordinated with the Br~(‥)onsted acid sites of γ-alumina. This may be the main driving force that improves appreciably the catalytic efficiency of Na_2CO_3/γ-Al_2O_3 catalyst.     

Surface chemical modification of zeolites and their catalytic performance for naphthalene alkylation

Acid-catalyzed naphthalene alkylation products, such as 2,6-dialkylnaphthalenes (2,6-DAN), are industrially important compounds used to make monomers for advanced polymer materials [1]. Zeolite molecular sieves can be extensively used in many catalytic applications, specifically in naphthalene alkylations due to their high activity and stability as well as their high selectivity. The initial studies have mainly focused on gas phase alkylation of naphthalene with methanol, and only obtained th…     

RESEARCH ON VIBRATION MODES OF THE CHINESE CHIME STONE

Nearfield acoustical holography is a powerful tool for imaging of acoustic sources. In this article, the basic theory treating steady-state acoustic radiation with generalized holography has been discussed. By holographic imaging, the vibration characteristics of irregular objects, the Chinese ancient musical instrument, the one-tone chime stone and the two-tone chime stone provided by the Institute of Archaeology, the Museum of Hubei Province, have been researched. The results show that the ancient chime stone has two main vibration modes, which make up the base of sound produced by the instrument. As for the two-tone chime stone, it is not so long and wide as the single-tone chime stone, but thicker and smoother than the single-tone chime stone. When it is excited at different positions, although it radiates sounds of different frequencies, its vibration modes are similar. This may be related to its dimensions and shape. The research is helpful for studying the sound producing system and the radiated field characteristics of the chime stone.