General features of nuclear tunneling in chemical reactions

1 GENERAL FEATURES OF NUCLEAR TUNNELING IN CHEMICAL REACTIONS 

In the present section, tunnel phenomena in elementary chemical reactions are considered. Most attention is paid to the tunneling of atoms. 

Bourgin [51] and Roginsky and Rosenkewitsch [52] were the first to pay attention to the possibility of the tunnel mechanism of chemical reactions. They did so quite soon after the creation of quantum mechanics. At that time, the main features of this phenomenon were also understood on the qualitative level. Later on, a large number of theoretical and experimental works were dedicated to more detailed studies on tunnel effects in chemical reactions. This field has attracted the interest of scientists up to the present time. A comprehensive review of the history and the present state of investigations of nuclear tunneling in chemical reactions can be found in the recently published monographs by Bell [53] and Goldanskii et al. [54], 

The simplest one-dimensional picture (Fig. 23) gives some ideas about nuclear tunneling during a chemical reaction. In the one-dimensional case, the probability of reaction can be given as 

In the classic case, the barrier is passed only by particles having an energy exceeding the height of the barrier E, E E0 and P = exp( — E0/T). If tunneling does not result in substantial (by one order of magnitude or more) increase of the reaction rate, then the averaged probability of the reaction can be expressed as 

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