COMPETITION BETWEEN BENZENE AND STYRENE IN FORMING RADICALS UNDER DIFFERENT SOLVENT CONDITIONS OBSERVED BY MUON LEVEL-CROSSING RESONANCE

The muon level-crossing-resonance technique has been used to resolve m ajor discrepancies that exist in muon-spin-resonance studies (both fre e-radical formation and muonium decay rates) in the competition betwee n benzene and styrene. The results, obtained for approximately 30 mM s olutions in ethanol and for 2.5 mM aqueous micelles solutions, show th at muonium atoms (Mu) react 8 (+/-2) times faster with styrene than wi th benzene. In the above cases thermalized Mu is unquestionably the re active species, which is known to show nucleophilic intra-molecular se lectivity in the case of styrene. But a similar value, 9 (+/-2), was a lso obtained for undiluted mixtures of liquid benzene and styrene (nea t mixture) - where the precursor might have been 'hot Mu' (which shoul d display weaker selectivity than Mu) or cations derived from mu+ (whi ch should show higher selectivity). These results support the view tha t thermalized Mu is the predominant reactive species in liquid benzene and styrene.