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相关概念视频

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration01:16

IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration

A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to the...

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相关实验视频

Updated: Jul 9, 2026

Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis
07:24

Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

Published on: May 10, 2021

直接观察Zn(CN) 2中负热膨胀的横向振动机制:一个原子对分布函数分析.

Karena W Chapman1, Peter J Chupas, Cameron J Kepert

  • 1School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia.

Journal of the American Chemical Society
|November 3, 2005
PubMed
概括

在Zn(CN) 2中,负热膨胀 (NTE) 是由桥的横向位移增加引起的. 这种结构性洞察力解释了NTE尽管个体债券扩张.

科学领域:

  • 材料科学 材料科学 材料科学
  • 固态化学 固态化学
  • 晶体学 晶体学是指结晶学.

背景情况:

  • 负热膨胀 (NTE) 材料具有独特的特性.
  • 了解NTE的原子层机制对于材料设计至关重要.
  • 化 (Zn(CN) 2) 是一种具有复杂框架结构的已知NTE材料.

研究的目的:

  • 为了研究Zn的即时原子结构.
  • 阐明Zn中负热膨胀的微观起源2.
  • 为了将结构动力学与宏观热膨胀行为相关联.

主要方法:

  • 原子对分布函数 (PDF) 的分析.
  • 高能X射线散射的实验. 高能X射线散射的实验.
  • 温度依赖的结构分析 (100-400K).

主要成果:

  • PDF分析显示,随着温度的增加,化物桥梁的横向位移增加.
  • 这种位移允许非最近邻近距离 (Zn...Zn', Zn...C/N) 的收缩.
  • 观察到个人债券长度 (Zn-C/N,C-N) 的扩大.

结论:

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Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis
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Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

Published on: May 10, 2021

Thermochemical Studies of Ni(II) and Zn(II) Ternary Complexes Using Ion Mobility-Mass Spectrometry
16:11

Thermochemical Studies of Ni(II) and Zn(II) Ternary Complexes Using Ion Mobility-Mass Spectrometry

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High-Speed Magnetic Tweezers for Nanomechanical Measurements on Force-Sensitive Elements
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High-Speed Magnetic Tweezers for Nanomechanical Measurements on Force-Sensitive Elements

Published on: May 12, 2023

  • 该研究证实,桥梁原子的平均位移增加是中NTE的起源.
  • 在较高温度下,NTE的轻微减少归因于相互透的框架相互作用.
  • 提供了Zn(CN) 2中NTE机制的最终结构证据.