The formation of a molecular radical following muon implantation in su
lphur S-8 is established experimentally by level crossing resonance. T
he position of the resonance determines the hyperfine constant as 233/-5 MHz. Of various possible assignments evaluated by ab initio molecu
lar orbital calculations, the most promising appears to be the muonic
sulfanyl radical, SMu. (C) 1997 Published by Elsevier Science.