Muonium Mu

Mu is a very light and unstable (ti/2 (half live) = 2 p,s) isotope of hydrogen consisting of a nucleus which is a positive muon (p,+) and an electron. The nuclear mass of Mu is 0.113 amu. For this isotope one would expect much larger KBoele values than those discussed above. 

The AC values for muonium hydrogen isotope effects are listed in Table 2.1. The AAC value obtained for LiH, H2 isotopic exchange involving Mu-H is 92 cm-1, 

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This paper is concerned with the structures of the simplest possible adducts of the Ceo and C70 fullerenes, namely the monohydrides, CmH and C H. These open shell species or radicals may be considered as the product of the addition of one atom of hydrogen or one of its isotopes, among which we include specifically the light pseudoisotope of hydrogen known as muonium. Mu = pfe. Although Ceo//has been observed [1], the stimulus for these calculations arose from the experiments on muon implantation in solid [2,3] and C70 [4]. 

Two types of species have been detected in the /rSR spectrum of Ceo- One shows an unreacted or meta-stable muonium state which may well correspond to an internal state, muonium is trapped inside the cage Mu Ceo in the current notation [2]. This may be compared with normal muonium (Mu ) in diamond and many other elemental and compound semi-conductors, where the trapping site is in one of the cavities of tetrahedral symmetry. This state of CeoMu is not discussed here, but it does exhibit all the characteristics expected of the internal chemistry of Ceo-The anomalous muonium state. Mu, observed in semi-conductors and generally accepted to arise from muonium being trapped within one of the chemical bonds of the crystal, is unknown in molecules [5,6]. The constraints of the crystal lattice are necessary for the bond-centred state to be stable. 

Note also the frequencies between 40 and 50 MHz observed in Si that are absent in quartz. This was the first observation of anomalous muonium (Mu ) in a semiconductor, and at the time of the discovery it was unexpected and unexplained (Brewer etal., 1973). In fact a cloud of controversy has surrounded Mu and its coexistence with Mu for almost 15 years. It isonly in the last two years that a consistent microscopic model of Mu has emerged. The lowest frequency line in Fig. 5, which occurs at the Larmor frequency of a bare muon, results from a diamagnetic center—Mu+ or Mu-. So far little is known about these muonium charge states. 

Anomalous Muonium (Mu ) a. Muon and 29Si Hyperfine Parameters... 

Much less is known about the charge states of muonium in silicon that are not neutral. The most likely ones of these are the positive and negative charge states, Mu+ and Mu. Both would have an even number of electrons and hence would quite likely be electronically diamagnetic. They presumably contribute to the p.SR line, usually labelled p+, which occurs at the Larmor frequency of a bare muon. Little else is known about these charge states other than that at high temperatures at least one of them is formed from neutral muonium, Mu and Mu. ... 

This simple treatment, formulated in a context of molecular bonding, was also what led Cox and Symons (1986) to propose the bond-center site as an explanation for anomalous muonium (Mu ). The location of the muon at the nodal plane of the nonbonding orbital explains the very small hyperfine coupling observed in pSR. Still, the muon is close to the electron, which occupies a nonbonding state on the neighboring semiconductor atoms. 

Muonium (Mu) is the lightest hydrogen-like atom (mMu = 0.11 mH) available for chemical research it has a positive muon (/jl+, t = 2.2 fisec) as the nucleus. The muon spin resonance (/tSR) technique is described in several review articles (16, 99—102). Most of the research is performed in the condensed phases, but because of the development of the surface muon beams (103, 104), experiments in the gaseous phase have received more attention. At present three muonic fractions can be detected (1) fan, free muonium (2) fa, free n+, or Mu bound in a diamagnetic compound and (3) fa, Mu bound in a paramagnetic compound. In liquid phases, there is quite often a missing fraction, fa = 1 -fau - fa - fa ... 

First of all what is muonium, what is its source, how do we observe it, and why is it useful Muonium (Mu) is an atom comprised of a positive muon nucleus, (y" ), and a bound electron. This bound electron can have its spin parallel or antiparallel to the muon nuclear spin resulting in triplet and singlet muonium atoms, respectively. The atom has a mass 1/9 that of the hydrogen atom, H but because the reduced masses are... 

Even more interesting of late is so-called "amomalous" muonium (Mu ), which produces the frequencies clearly observable in Figure 16 at 15, 40 and 48 MHz, and in Figure 5 at similar frequencies. 

Mu + H2 Muonium (Mu) is an isotope of the hydrogen atom with a positive muon as the nucleus. Since it is 8.8 times lighter than H, tunnelling and zero point effects are enormous, and in fact the Mu +... 

In muonium chemistry, hot muonium (Mu ) has been used for its similarity to hot hydrogen. Senba et al. (2000) studied hot atom reaction yield in Mu + H2, and T + H2 from quasiclassical trajectory cross sections on the Liu-Siegbahn-Truhler-Horowitz surface. Other examples are described in Chap. 28 on Exotic Atoms and Muonium in this Volume. 

The atoms formed by a positive particle and an electron (such as positronium, Ps = e e or muonium. Mu = p e ) also belong to the family of exotic atoms, and owing to the wide applications of positron aimihilation and muon spin research in solid-state physics and chemistry, their study is much more intensive than that of the exotic atoms with negative particles. Also, the physical processes are quite different for exotic atoms with negative and positive particles. As positron annihilation and spectroscopy are treated separately in 0 Chap. 27, this chapter is restricted to exotic atoms with negative particles and with the positive muon. 

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