Properties of the Transition State

 
Determination of the second derivatives of the Potential Energy Surface (PES) along three sections, and for the bending motions. Here the 'V' term is the difference from the energy of the TS (printed in truncated form). It is negative in the H-H direction, because this is near the trajectory over the saddle point. The 'check' numbers test the validity of the harmonic approximation. The four numbers different from 0 in every section should be approximately equal. The same applies to the five terms 'V/Phi^2' in the bending motions.

 
This is the output of the computation of the force constants for the triatomic transition state. It has been verified that the potential is sufficiently harmonic around the locus of the TS. The asymmetric stretch is the motion on the reaction coordinate. The curvature over the saddle point is negative, therefore we obtain an imaginary frequency. Since the partition function of the transition state takes the motion of the activated complex over the saddle point as an internal translation explicitely into account, we exclude the asymmetric stretch from its vibrational partition function and from the zero point energy. Notice that the bending motion is doubly degenerate. The program allows to study the effects of isotope substitution on the rate constant.