Intrinsic reaction path energy profile

The energy variations along the intrinsic reaction path (IRP) and the ADMP trajectory are reported in Figures 2 and 3, respectively. We want to underline that the IRP corresponds to a unique and constrained minimum energy path and does not contain any time information, whereas the ADMP profile is computed along a trajectory issued by a dynamics simulation. Therefore, any direct (i.e. point-to-point) comparison is misleading. Nevertheless, their global differences can be discussed. 

Figure 8. Energy profile along the intrinsic reaction paths for reaction (3.15), shown relative to the energy of the formaldehyde radical cation (see Refs. 56 and 57). There are two separate routes for the dissociation of structure 1 through to a weak complex in the product valley, structure S. The paths were calculated at the Hartree-Fock/6-31G level of theory. The molecular structures at the stationary points on the paths are sketched.

The top of the profile is maximum (saddle point) and is referred as the transition state in the conventional transition state theory. It is called a saddle point because it is maximum along the orthogonal direction (MEP) while it is minimum along diagonal direction of Fig. 9.12. The minimum energy path can be located by starting at the saddle point and mapping out the path of the deepest descent towards the reactants and products. This is called the reaction path or intrinsic reaction coordinate. 

Figure 7. Energy profile along the IRP for reaction (3.14) (see Ref. 41). The path was calculated at the Hartree-Fock/6-31G(d, p) level and the energy (in a.u.) is shown relative to that of the separated leactants. The intrinsic reaction coordinate has units of amu" bohr. BR denotes the location of a branching point. The geometries at the minimum in the reactant valley and at the saddle point are sketched.

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