Potential energy surfaces

Consider letting go of a single mass placed on a smooth frictionless surface with various extrema.  Using reduced mass coordinates, a collinear triatomic system can be reduced to just that, a single mass on a potential energy surface. The three atoms and their relative coordinates x and y are shown here.

A contour plot for a typical reaction AB+C→ A+BC is shown below. The star is a saddle point called the transition state, it is where the exchange reaction takes place.

Many surfaces are derived via Born-Openheimer calculations.  From Unimolecular reactions, eximers, macromolecular mechanisms, and electronic bifurcations potential energy surfaces are a powerful way to reveal what is going on during molecular interactions.  In my case will stay on a bimolecular reaction surface.  This surface includes reactant and product channels. For example, here is a triple Hydrogen potential energy surface calculated from a famous Fortran program.  The distances are in angstroms and the energy is in decaHartrees.

A major point to be made here is that we focus on adiabatic electronic transitions. Non-adiabatic molecular dynamics introduces multiple surfaces.


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