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.

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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.************