Muons as Sensitive Isotopic H-atom Probes of Quantum Mass Effects in Chemical Reactivity and of the Motion of Muoniated Free Radicals in Nanoparticle Environments.

化学反应速率的研究是整个化学领域的中心，在这项研究中，往往是复杂机制中最简单的基本步骤是最重要的。其中最主要的是氢原子及其同位素变体的反应速率;质量为2 amu的氘（D）是最为人所知的。同位素具有相同的电子数，但核质量不同。另一种常见的氢同位素是氚（T），质量为3 amu，但具有危险的放射性，在热反应速率的研究中几乎没有使用。因此，扩展同位素氢原子质量尺度的任务就落到了核科学，特别是μ介子科学的肩上。氢原子最轻的同位素是μ 鎓 **（Mu= u+e-），其中“u+”是一个正μ子，质量只有质子的1/9。虽然缺乏传统意义上的“核”，μ子质量仍然是电子质量的200倍，这意味着 **Mu和H原子表现出相同的化学性质，但由于它们的质量相差 ** 9倍，反应速率非常不同。这个应用程序关注的是新的方向在穆反应性从状态-** 选择反应物，使用激光填充分子激发态。在质量标度 ** 的另一端是μ子He原子（4 Heu），其中来自TRIUMF加速器的负μ子被 ** 氦原子捕获，在此过程中取代一个电子，从而赋予4 Heu 4.1 amu的质量，这是H原子的 ** 最重的同位素。我们现在能够比较Mu和4 Heu ** 在质量因数为36的前所未有的比率上的反应速率，这也是本申请的关键方面。我们研究Mu反应性的一个可能的实际方面是“μ离子化自由基”的形成，特别是它们在重要的工业催化剂如Zeolite中的运动效应，对此没有其他技术可以产生同样详细的结果。这也是本申请的一个重要方面，** 但扩展到其他环境，Au纳米颗粒上μ离子化自由基的研究。*

The study of chemical reaction rates is central to the whole field of chemistry and in this study it is often **the most simple elementary steps in a complex mechanism that are the most important. Chief among these **are the reaction rates of the H-atom and its isotopic variants; deuterium (D), with a mass of 2 amu, being **the most well known. Isotopes have the same number of electrons but different nuclear masses. Another **common hydrogen isotope is tritium (T), with a mass of 3 amu, but being dangerously radioactive, it has **seen little use in the study of thermal reaction rates. Thus it has fallen to nuclear science and particularly **muon science to extend the isotopic H-atom mass scale. The lightest isotope of the H-atom is Muonium **(Mu= u+e-), where `u+' is a positive muon, with a mass only 1/9th that of the proton. Though lacking a **"nucleus'' in the conventional sense, the muon mass is still 200 times the electron mass, meaning that **Mu and H atoms exhibit the same chemistry, but with very different reaction rates due to their factor of **nine difference in mass. This application is concerned with new directions in Mu reactivity from state-**selected reactants, using lasers to populate molecular excited states. At the other end of the mass scale **is the Muonic He atom (4Heu), where negative muons from the TRIUMF accelerator are captured by a **Helium atom, replacing one electron in the process, thereby endowing 4Heu with a mass of 4.1 amu, the **heaviest isotope of the H-atom. We are now in a position to compare the reaction rates of Mu and 4Heu **over an unprecedented ratio of a factor of 36 in mass, also a key aspect of the present application. A **possible practical aspect of our study of Mu reactivity is the formation of ''muoniated radicals'' and in **particular their motional effects in important industrial catalysts like Zeolites, for which there is no other **technique that can yield the same detailed results. This too is an important aspect of the present application,**but extended to other environments, the study of muoniated radicals on Au nanoparticles.************