Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
Laboratoire de Tribologie et Dynamique des Systèmes, CNRS UMR5513, Ecole Centrale de Lyon, F-69134 Ecully cedex, France.
Phys Chem Chem Phys. 2023 Jun 15;25(23):15855-15861. doi: 10.1039/d3cp00980g.
Mechanochemical reaction pathways are conventionally obtained from force-displaced stationary points on the potential energy surface of the reaction. This work tests a postulate that the steepest-descent pathway (SDP) from the transition state to reactants can be reasonably accurately used instead to investigate mechanochemical reaction kinetics. This method is much simpler because the SDP and the associated reactant and transition-state structures can be obtained relatively routinely. Experiment and theory are compared for the normal-stress-induced decomposition of methyl thiolate species on Cu(100). The mechanochemical reaction rate was calculated by compressing the initial- and transition-state structures by a stiff copper counter-slab to obtain the plots of energy slab displacement for both structures. The reaction rate was also measured experimentally under compression using a nanomechanochemical reactor comprising an atomic-force-microscopy (AFM) instrument tip compressing a methyl thiolate overlayer on Cu(100) (the same system for which the calculations were carried out). The rate was measured from the indent created on a defect-free region of the methyl thiolate overlayer, which also enabled the contact area to be measured. Knowing the force applied by the AFM tip yields the reaction rate as a function of the contact stress. The result agrees well with the theoretical prediction without the use of adjustable parameters. This confirms that the postulate is correct and will facilitate the calculation of the rates of more complex mechanochemical reactions. An advantage of this approach, in addition to the results agreeing with the experiment, is that it provides insights into the effects that control mechanochemical reactivity that will assist in the targeted design of new mechanochemical syntheses.
机械化学反应途径通常是从反应势能面上力位移的固定点获得的。这项工作检验了一个假设，即从过渡态到反应物的最陡下降途径（SDP）可以合理地准确用于研究机械化学反应动力学。这种方法要简单得多，因为 SDP 及其相关的反应物和过渡态结构可以相对常规地获得。实验和理论对甲基硫醇物种在 Cu(100)上的正向力诱导分解进行了比较。机械化学反应速率是通过压缩初始态和过渡态结构来计算的，方法是使用一个刚性铜对板来压缩初始态和过渡态结构，从而获得这两种结构的能量与板位移的关系图。反应速率也通过使用原子力显微镜（AFM）仪器针尖压缩 Cu(100)上的甲基硫醇覆盖层的纳米机械化学反应器在压缩下进行实验测量（与进行计算的相同系统）。通过在甲基硫醇覆盖层的无缺陷区域上形成的压痕来测量速率，这也可以测量接触面积。知道 AFM 针尖施加的力可以得到作为接触应力函数的反应速率。结果与理论预测吻合良好，无需使用可调参数。这证实了该假设是正确的，并且将促进更复杂的机械化学反应速率的计算。除了实验结果吻合外，这种方法的一个优点是，它提供了控制机械化学反应性的影响的见解，这将有助于有针对性地设计新的机械化学合成。
