STUDIES ON DYNAMICS OF MU-REACTION WITH NO2 BY MUON SPIN-RESONANCE AND RELAXATION TECHNIQUES

The reaction of Mu with NO2 in a Kr atmosphere was studied by muon spi n resonance and relaxation measurements at 300 K. It was found that th e reaction proceeds via the following two steps: Mu+NO2-->MuO+NO and M uO+NO2-->MuNO(3). In particular, the final product MuNO(3) and the int ermediate species MuO were successfully detected for the first time by the techniques of the muon spin resonance and the longitudinal relaxa tion under a high magnetic field of similar to 2800 G. The rate consta nts of the Mu+NO2 and the MuO+NO2 reactions were determined to be (2.9 +/-0.5)X10(11) e mol(-1) s(-1) and (4.5+/-0.1)X10(9) e mol(-1) s(-1) a t 300 K. The isotope effect in the rate constant of the Mu+NO2 reactio n in comparison with the H+NO2 reaction suggests that there are reacti on paths with a slight energy barrier which is high enough to retard t he H reaction, but not the Mu reaction. On the other hand, the rate co nstant of the MuO+NO2 reaction is smaller than 50% of those of the OHNO2 and the OD+NO2 reactions. This isotope effect seems to originate f rom faster rotational motion of MuO and/or lower vibrational density o f states at the transition state.