Basis sets tunneling effects

The application of isotope effects studies of reaction mechanism includes comparison of experimental values of isotope effects and predicted isotope effects computed for alternative reaction pathways. On the basis of such analysis some of the pathways may be excluded. Theoretical KIEs are calculated using the method of Bigeleisen and Mayer.1 55 KIEs are a function of transition state and substrate vibrational frequencies. Equilibrium isotope effects are calculated from substrate and product data. Different functionals and data sets are used in these calculations. Implementation of a one-dimensional tunnelling correction into conventional transition-state theory significantly improved the prediction of heavy-atom isotope effects.56 Uncertainty of predicted isotope effect can be assessed from the relationship between KIEs and the distances of formed or broken bonds in the transition states, calculated for different optimized structures.57 Calculations of isotope effects from sets of frequencies for optimized structures of reactants and transition states are facilitated by adequate software QUIVER58 and ISOEFF.59... 

Again, this effect can be understood in terms of the templating of hyperbolic structures, due to the presence of hyperbolic TFS, set up by the caesium ions in solution. For example, the carcerand molecule resides on the P-surface (Fig. 2.21), which is a common TFS in aqueous zeolite syntheses. The improved yield of large ring compoimds in the presence of cesium is also understandable on this basis, since the precursors to these compounds prefer to wrap around tunnels of the TFS [13]. 

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