The CH3 tunnelling sidebands of Δm=0 studied by dipole-dipole driven low-field NMR in the frequency domain
The CH3 tunnelling sidebands of Δm=0 studied by dipole-dipole driven low-field NMR in the frequency domain
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频域偶极-偶极驱动低场核磁共振研究Δm=0的CH3隧道边带
DOI：
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发表时间：
1989
期刊：
影响因子：
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通讯作者：
A. Aibout
中科院分区：
文献类型：
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作者：
A. J. Horsewill;A. Aibout
用低场偶极-偶极驱动的核磁共振谱在频域中记录了含有隧穿分子基团的材料。在苯硫醚和2-丁酮中的甲基分别具有557+或-3kHz和491+或-3kHz的隧穿频率。除了Δ m=+或-1和Δ m=+或-2的边带之外，在隧道频率处清楚地观察到Δ m=0的隧穿边带，并且首次报道。所有边带的强度都具有相似的量级。Δ m=0的边带是由RF场引起的跃迁引起的，其中甲基经历了隧穿状态的变化，而总体自旋没有变化。尽管如此，在质子磁化强度与频率的关系图中观察到边带。提出了一个热力学模型来解释磁化强度的变化是如何产生的;作为场循环序列的一部分遇到的水平交叉点负责将隧道水库中的无序转移到塞曼水库中的无序。讨论还集中在负责驱动的低场光谱中揭示的过渡的机制。
The low-field dipole-dipole driven NMR spectra of materials that contain tunnelling molecular groups have been recorded in the frequency domain. The methyl groups in thioanisole and 2-butanone have tunnelling frequencies of 557+or-3 kHz and 491+or-3 kHz respectively. In addition to the sidebands of Delta m=+or-1 and Delta m=+or-2, tunnelling sidebands of Delta m=0 are clearly observed at the tunnel frequency and are reported for the first time. The intensities of all the sidebands are of similar magnitude. The sidebands of Delta m=0 result from transitions induced by the RF field in which the methyl group undergoes a change in tunnelling state without a change in overall spin. Despite this, the sidebands are observed in a plot of proton magnetisation versus frequency. A thermodynamic model is proposed to explain how the change in magnetisation is generated; level crossings encountered as part of the field cycling sequence are responsible for transferring disorder in the tunnel reservoir into disorder in the Zeeman reservoir. Discussion also centres upon the mechanism responsible for driving the transitions revealed in the low-field spectra.