Potential energy surfaces Born-Oppenheimer construct

Nevertheless, very-long-lived quasi-stationary-state solutions of Schrodinger s equation can be found for each of the chemical structures shown in (5.6a)-(5.6d). These are virtually stationary on the time scale of chemical experiments, and are therefore in better correspondence with laboratory samples than are the true stationary eigenstates of H.21 Each quasi-stationary solution corresponds (to an excellent approximation) to a distinct minimum on the Born-Oppenheimer potential-energy surface. In turn, each quasi-stationary solution can be used to construct an alternative model unperturbed Hamiltonian //(0) and perturbative interaction L("U),... 

Chemical dynamics is the link between the potential energy surface (PES) (or surfaces) and an observable chemical phenomena. In principle the PES comes from an ab initio quantum chemistry calculation (within the Born-Oppenheimer approximation) though in practice it is often constructed by some more approximate model, e.g., semiempirical quantum chemistry or totally empirical force field models. First a brief overview of the present state of the methodology and scope of applications in this area is given. We will concentrate on chemical dynamics in the gas phase, though much of the methodology of this field has carried over to the study of dynamical processes in condensed phases, gas-surface collision processes, and also dynamics in biomolecular systems. 

The potential energy is illustrated in Fig. 6.3a. While one can in principal calculate the exact quantum mechanical Born-Oppenheimer surface, the figure presents a semi-empirical surface constructed to yield the exact spectral properties of reactants and products and the correct activation energy (taken as the difference in energy between the energy (potential) in the reactant valley (x = oo) and the maximum of the MEP (minimum energy pathway).)... 

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