Ra. Marcus, GLOBAL POTENTIAL-ENERGY CONTOUR PLOTS FOR CHEMICAL-REACTIONS - STEPWISE VS CONCERTED 2+2 CYCLOADDITION, Journal of the American Chemical Society, 117(16), 1995, pp. 4683-4690
A global contour plot is described for reactions involving stepwise or
concerted addition of two ethylenes to form cyclobutane. The relevant
isomers of the various species and of the reaction paths, with plains
or valleys, minima, saddle points, and domes or conical intersections
, are described. Two collective asymmetric coordinates are introduced
as axes for the plot, which presents an overview of the system and whi
ch complements the usual 2-dimensional cuts of the many-dimensional po
tential energy surface. Other global coordinates are also introduced.
The plot involves a pointwise minimization of the potential energy wit
h respect to the coordinates not used as axes. A permutation symmetry
can be used to derive the various coordinates. Free energy and entropy
(or number of states) curves versus a reaction coordinate are discuss
ed.