MU-SR STUDIES OF FREE-RADICALS IN THE GAS-PHASE

Muonium (Mu=mu(+)+e(-)) is the bound state of a positive muon and an e lectron. Since the positive muon has a mass about 1/9 of the proton, M u can be regarded as an ultra light isotope of hydrogen with unusually large mass ratios (Mu:H:D:T=1/9:1:2:3). The muon spin rotation techni que (mu SR) relies on the facts that (1) the muon produced in pion dec ay, pi(+) --> mu(+) nu(mu), is 100% spin polarized and (2) the positro n from muon decay is emitted preferentially along the instantaneous mu on spin direction at the time of the muon decay. In transverse field m u SR (TF-mu SR), the precession of the muon spin in muonium substitute d radicals is directly observed by detecting decay positrons time diff erentially. From observed radical frequencies, the hyperfine coupling constants (A(mu)) of C(2)H(4)Mu, C(2)D(4)Mu, (13)C(2)H(4)Mu, C(2)F(4)M u, and C(2)H(3)FMu are determined. In the longitudinal field avoided l evel crossing (LF-ALC) technique, one observes the resonant loss of th e muon spin polarization caused by the crossing of hyperfine levels at particular magnetic fields. The LF-ALC method together with the infor mation on A(mu) obtained from TF-mu SR allows one to determine the mag nitude and sign of the nuclear hyperfine constants at alpha- and beta- positions. Results are compared with hydrogen substituted ethyl-radica ls and isotope effects are discussed.