Hyperfine anisotropy and crystal field effects in Mu adducts to naphthalene

Muonated cyclohexadienyl type radicals have been studied in a naphthalene single crystal using the standard transverse-field μSR technique. Muonium addition occurs at both the α and the β positions. Because of the multiplicity and weakness of the lines in the Fourier spectrum, special techniques were developed to allow the signals to be found and identified. The isotropic hyperfine coupling constants show large shifts from the solution values, with significant anisotropy in the hyperfine tensors. The results for the α radicals are similar to those observed for protonated α-hydronaphthyl radicals, but isotope effects are evident. Based on the hyperfine tensor directions and geometrical considerations, each radical has been assigned to a specific muon site within the crystal.