Frantsuzov I, Johnson M R, Trommsdorff H P, Horsewill A J
School of Physics & Astronomy, University of Nottingham , Nottingham NG7 2RD, U.K.
J Phys Chem B. 2014 Jul 17;118(28):7777-84. doi: 10.1021/jp410889x. Epub 2014 Jan 28.
Field-cycling (1)H NMR relaxometry has been used to measure the rate of concerted double proton transfer in the hydrogen bonds of (16)O and (18)O isotopologues of benzoic acid dimers. The experiments have been conducted in the solid state at low temperature 13.3 ≤ T ≤ 80 K where the dynamics are dominated by incoherent proton tunnelling. The low temperature tunnelling rate in the (16)O isotopologue is observed to be approximately 15% faster than in the (18)O isotopologue. The difference is attributed to an isotope effect of the heavy atom framework of the benzoic acid dimer resulting from displacements of the oxygen atoms that accompany the proton transfer. Sources of systematic uncertainty have been minimized in the design of the experimental protocols and the experiments are critically appraised in formally assigning the measured differences to an effect of mass on the tunnelling dynamics.
场循环（1）H核磁共振弛豫测量法已被用于测量苯甲酸二聚体的（16）O和（18）O同位素异构体氢键中协同双质子转移的速率。实验在低温13.3≤T≤80K的固态下进行，此时动力学主要由非相干质子隧穿主导。观察到（16）O同位素异构体的低温隧穿速率比（18）O同位素异构体快约15%。这种差异归因于苯甲酸二聚体重原子骨架的同位素效应，该效应由质子转移伴随的氧原子位移引起。在实验方案的设计中，系统不确定性的来源已被最小化，并且在将测量到的差异正式归因于质量对隧穿动力学的影响时，对实验进行了严格评估。
