Detection of a secondary muoniated radical

Muoniated free radicals are formed by addition of muonium to unsaturated molecules. Successful detection by transverse-field muon spin rotation (mu SR) usually requires pure or highly concentrated samples and a muonium reaction rate in excess of 109 M(-1)s(-1) to ensure that the muon spin polarization is coherently transferred to the radical. For this reason muoniated radicals reported to date are all the primary radical products of Mu reaction. Thus, it was expected that Mu addition to a silylene would result in detection of a silyl radical. However, the muon hyperfine constant determined by experiment is much smaller than the value predicted by density functional calculations. instead, it is consistent with a disilanyl radical, the secondary radical formed by reaction of the initially formed silyl radical with a second silylene molecule. From an analysis of the signal amplitude it was deduced that the second-order rate constant for reaction of the muoniated silyl radical with the parent silylene is 5.7 x 10(-8) M(-1)s(-1). This work represents the first example of direct detection of a secondary radical product by transverse-field mu SR. (c) 2008 Elsevier B.V. All rights reserved.