Predissociative potentials intramolecular

Zhao and Rice extended the above-sketched Gray-Rice theory to include the effects of intramolecular energy transfer, using analytical approximations for various quantities [15]. Because this extension is in the same spirit as in the case of unimolecular predissociation, the Zhao—Rice approximation presented here is still called the MRRKM theory. Zhao and Rice employed a model double-well potential similar to that used by Gray and Rice, but parameterized to have greater flexibility. Specifically, the three terms in the potential of Eq. (201) are taken to have the following form ... 

In this expression Q = 0 at the equilibrium configuration of the free polyatom. The first term gives the van der Waals potential at the free molecule equilibrium positions of the polyatom nuclei. This term cannot couple different polyatom vibrational states, however, so it does not contribute directly to vibrational predissociation. The second and third terms are written as derivatives of the van der Waals potential with respect to displacements in the polyatom coordinates, but they can also be viewed as changes in the intramolecular potential in the presence of the adatom. We can make the physical meaning of Eq. (II.6) clearer by rewriting it as... 

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