Muonium addition to pyrene has been investigated by means of transverse fie
ld muon spin rotation and muon level-crossing spectroscopy. Two hydropyreny
l radicals are produced and easily detected while a third is formed in low
abundance. Muon and proton hyperfine constants were experimentally determin
ed and compared with semiempirical and ab initio calculations. It is conclu
ded that the radicals are of cyclohexadienyl type, i.e., the Mu adds only t
o carbon atoms that can assume a tetrahedral -CHMu- configuration without d
istorting the planar carbon skeleton of pyrene.