Statistical adiabatic channel model cases

E.LDashevskaya, E.E.Nikitin and J.Troe, Nonadiabatic effects in the statistical adiabatic channel model the atom + diatom case, J. Chem. Phys. 97, 3318 (1992)... 

In the limit of high pressure, collisions maintain the thermal distribution of reactant molecules over their internal energy states and consequently TST can be used to determine the thermal rate constants for dissociation and association. However, in the case where there is no maximum in the reaction path leading from reactants to products, it is necessary to take account of angular momentum (/) constraints as well as internal energy. The transition state is not found at a single separation but rather it depends on Eint and J. Then, in the language of the statistical adiabatic channel model (SACM), the partition function for the transition state can be expressed as ... 

When the interaction depends on the orientation of the neutral molecule, as is the case, for example, for ion-dipole reactions, the simple treatment outlined above is no longer appropriate. The adiabatic channel method is often used in this context [32]. The rotational energy levels in the separated reactants are coupled with the orbital energy levels to define a set of channels for the collision complex. The number of open states, N(EJ), is the number of channels with an energy maximum below the energy E. Examples of this approach include the adiabatic channel centrifugal sudden approximation (ACCSA) of Clary [33] and the statistical adiabatic channel model (SACM) of Troe and co-workers [34]. 

Statistical methods represent a background for, e.g., the theory of the activated complex (239), the RRKM theory of unimolecular decay (240), the quasi-equilibrium theory of mass spectra (241), and the phase space theory of reaction kinetics (242). These theories yield results in terms of the total reaction cross-sections or detailed macroscopic rate constants. The RRKM and the phase space theory can be obtained as special cases of the single adiabatic channel model (SACM) developed by Quack and Troe (243). The SACM of unimolecular decay provides information on the distribution of the relative kinetic energy of the products released as well as on their angular distributions. 

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