Horsewill A J, Jones N H, Caciuffo R
School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.
Science. 2001 Jan 5;291(5501):100-3. doi: 10.1126/science.291.5501.100.
We observed coherent proton tunneling in the cyclic network of four hydrogen bonds in calix[4]arene. The tunneling frequency of 35 megahertz was revealed by a peak in the magnetic field dependence of the proton spin-lattice relaxation rate measured with field-cycling nuclear magnetic resonance in the solid state at temperatures below 80 kelvin. The amplitude of the coherent tunneling peak grows with temperature according to a Boltzmann law with energy D/kB = (125 +/- 10) kelvin (where kB is Boltzmann's constant). The tunneling peak can be interpreted in the context of level crossings in the region where the tunneling frequency matches the proton Larmor frequency. The tunneling spectrum reveals fine structure that we attribute to coupling between the hydrogen bonds in the network. The characteristics of the tunneling peak are interpreted in the context of the potential energy surface experienced by the hydrogen atoms in the network.
我们在杯[4]芳烃中由四个氢键构成的环状网络中观察到了相干质子隧穿。通过在低于80开尔文的固态温度下利用场循环核磁共振测量质子自旋 - 晶格弛豫率的磁场依赖性中的一个峰，揭示了35兆赫兹的隧穿频率。相干隧穿峰的幅度根据能量为(D/k_B = (125 ± 10))开尔文的玻尔兹曼定律随温度增长（其中(k_B)是玻尔兹曼常数）。在隧穿频率与质子拉莫尔频率匹配的区域内，可以根据能级交叉的情况来解释该隧穿峰。隧穿谱揭示了精细结构，我们将其归因于网络中氢键之间的耦合。根据网络中氢原子所经历的势能面来解释隧穿峰的特征。
