Temperature dependence of the muon and proton hyperfine constants of an alpha‐muonium‐substituted methyl radical

Muon hyperfine constants A_μ have been measured by transverse field μSR for (CH₃)₃Simbox.CHMu in hexane from 167 K to 332 K. In addition, avoided level‐crossing resonance was used to determine alpha‐proton coupling constants A_p over a similar range of temperatures. The two hyperfine constants can be described by a common temperature dependence, d|A_i|/ dT=1.4times 10^-3 MHz,K^-1, where A_i represents A_p or the reduced muon constant A^prime_μ=0.3141A_μ. There is a small isotope effect (A^prime_μ is 2.2 % larger than A_p) consistent with zero‐point motion in the anharmonic C–H bond stretch. The common temperature dependence is tentatively attributed to a coupled deviation of the C–H and C–Mu bonds out of the nodal plane of the p orbital containing the unpaired electron. This revised version was published online in August 2006 with corrections to the Cover Date.