Example #1: HOBr -> HBrO

2 minima and 1 isomerization transition state

note - there are 3n-6 = 3 degrees of freedom, so we already have to chose which 2 coordinates to view at one time
(2 internal coordinates + the potential energy). The figures below are for fixed r(BrO) = 3.34 a.u. Consider that to
generate the full global potential energy surface for this system from which these cuts were extracted required over
1,000 separate ab initio calculations (one per nuclear arrangement) !

Surface plot (energy in kcal/mol relative to a zero of energy at the H+O+Br asymptote):

As you can tell, visualizing potential energy surfaces by these types of plots are very dependent on the viewing angle and
are not very convenient (but sometimes look cool). A more quantitative method is to use contour plots:

Example #2: A simple bimolecular reaction surface: the collinear F + H₂ -> HF + H abstraction reaction

The reaction occurs on a 3-dimensional hypersurface of doublet Sigma+ symmetry (linear molecule label)
completely analogous to a triatomic molecule.
In the following plots the 2-dimensional cut is restricted to collinear approaches (a F-H-H angle of 180 degs.).

Surface plot (in kcal/mol with a zero of energy at the F+H₂ reactants):

Note: the level of ab initio theory here is certainly not sufficient for a quantitative description, but has the
correct qualitative form (the actual barrier height is about 1.8 kcal/mol). This PES vastly overestimates the
barrier height (14 vs. 1.8) and underestimates the exothermicity (~20 vs. 32).

Contour plot of the same data: