Bond-switching-mode frequency

Figure L The generalized-normal-mode frequency for the bond-switching mode as a function of reaction coordinate for OH + NH3 —> H2O + NH2-...

Figure 5.12 depicts the corresponding adiabatic one-dimensional potential for the covalent rHF proton-transfer coordinate, showing the barrierless switch-over at equilibrium between FH F and F HF bond patterns. The potential well is seen to be extremely flat in the neighborhood of equilibrium, corresponding to the extremely low IR frequency of the proton-transfer mode (1299 cm-1, red-shifted... 

The assumption that the vibrational frequencies of the transitional modes decrease with R in an exponential manner is common to a number of the more sophisticated RRKM formulations. The exponential function is one of several switching functions that have been proposed to take into account the fact that several frequencies change dramatically in going from the molecule to products. However, these switching functions add new variables which ultimately become empirical fitting parameters. The a, s in the exponential function differ for different types of bonds and they also differ for neutral and ionic reactions. For instance, theoretical studies have shown that for neutral... 

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