Muons as hyperfine interaction probes in chemistry

How intrinsic nuclear nonadiabaticity affects molecular structure, electronic density, and conformational stability: Insights from the multicomponent DFT calculations of Mu/H isotopologues

“…This has been made possible by the early theoretical and technical developments of muon spin spectroscopy to study muon spin rotation, relaxation, and resonance commonly known as μSR spectroscopy [27] . The thermalization of a positive muon would lead to the formation of muonium (Mu) atom, discovered experimentally by Hughes et al in 1960, which is conceived as a lighter isotope of hydrogen [28][29][30][31][32][33] . This is further established in the light of the comparative chemical kinetic investigations and recent theoretical studies regarding the "independent chemical identity" of the muonium atom with respect to the other members of the Periodic Table [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] .…”

Influence of confinement on free radical chemistry in layered nanostructures

“…The kinetics of elementary reactions is the best probe of the effects of confinement on chemical dynamics; the most sensitive probe of confinement effects on electronic structure is the one that measures the electron density. The isotropic hyperfine coupling constant (HFCC) is very efficient in this regard 15–20 . It measures the strength of the coupling between unpaired electrons with the nuclear magnetic moment.…”

“…For this purpose, a good starting point is to study the effects of confinement on the H atom, which is the most fundamental entity in chemistry. Indeed, investigation of H atom and its isotopes has played a fundamental role in the evolution of modern science 14–20,27–32 ; as such, determining the behavior of H atom in various environments is crucial in the development of dimensionally constrained systems such as heterogeneous catalysts 31 , nanometer-scale semiconductors 32 , and hydrogen storage devices 29 .…”

“…It requires a technique that: i) can be used at any temperature; ii) is not limited by optical detection (as it is impossible for clays); iii) is time-resolved to be able to detect short-lived species; and iv) can provide the electronic structure of the free radicals. The only way to fulfill all above criteria is to use the hydrogen surrogate, muonium, and positive muon-based spectroscopic techniques as the positive muon (µ + ) (called hereafter muon) is an exotic particle behaving as a light proton (H + ) 19,20,44 .…”

“…Muonium (Mu ≡ μ + e − ), obtained after capture of an electron by a muon, has one-ninth of the mass of H with almost the same Bohr radius (0.53 Å) and ionization energy (13.539 eV for Mu and 13.598 eV for H) 20 . Because Mu is electronically equivalent to an H atom, it can be used as a surrogate of the latter when it cannot be studied directly 45 .…”