Heavy particles tunneling mechanisms

At present, the model of solid-state chemical reactions suggested in the literature [48-50] has won certain recognition. McKinnon and Hurd [152] and Siebrand and co-workers [153] compare the mechanism of rate constant temperature dependence by the occupation of the highest vibrational sub-levels of the tunneling particle to that of fluctuation preparation of the barrier the latter Siebrand et al. is preferred. [153] particularly emphasize the experimental proof of the linear dependence of the rate constant logarithm on the temperature predicted by this model. The importance of an account for intermolecular vibrations in the problem of heavy-particle tunneling [48-50] is also noted elsewhere [103]. 

Tunneling plays a role for atomic particles. If one considers heavy particles, then the results obtained from Eq. (6.34) will be indistinguishable from the step function predicted by classical mechanics,... 

Unfortunately, the quantum-mechanical tunneling approach does not lead to any better understanding of why a should be temperature dependent in many reactions, if only for the reason that in most of the cases where such behavior is observed, the reactions involve heavy particles for which quantum effects are negligible. O2 reduction, however, could be quantally controlled if... 

Although the effects related to the proton tunneling and to the non-equilibrium nature of the coordinate of heavy particles are essentially quantum-mechanical, they noticeably differ in their mechanism. For this reason we prefer to retain the term "barrierless for processes in which the intermediate product stabilizes only due to a low proton tunneling probability from its ground state (in principle we could also include here the processes with a low electron transition probability), applying the term "quasibarrierless" to the second type of processes. 

---