Isotope effect on unimolecular dissociation of MuO(2): a classical trajectory study

Classical trajectory calculations have been carried out for the unimolecula r dissociation of both rotating and non-rotating MuO(2) (Mu = muonium hydro gen isotope analog) over the total internal energy range 55.432 less than o r equal to E-tot/kcal mol(-1) less than or equal to 72.282. For the non-rot ating system, various distributions of energy among the three vibrational n ormal modes have been considered, while in the rotating case, 5 kcal mol(-1 ) of rotational energy has been associated to the principal axis of inertia in four different ways. The calculations employed the realistic DMBE IV po tential energy surface for the electronic ground state of HO2, which allows an assessment of the isotope effects by comparison with our previous work (J. Phys. Chem. A, 1997, 101, 5168). Unlike previous results for HO2, the r eaction MuO(2) --> Mu + O-2 shows more than one decay regime even in the ab sence of rotation. This non-RRKM-type behavior appears to be intrinsic, and has been attributed to the large difference between the Mu-O-2 vibrational frequency and those of the other two modes. Inclusion of rotation leads al so to deviations from RRKM-type behavior, especially when rotational excita tion is associated to the adiabatic L-y and L-z axes of inertia. The role o f the MuO(2) and HO2 zero-point energies is also analysed.