Mv. Basilevsky et Mv. Vener, COLLECTIVE MEDIUM COORDINATES AND THEIR APPLICATION IN THE THEORY OF CHEMICAL-REACTIONS, Journal of molecular structure. Theochem, 398, 1997, pp. 81-92
A collective medium coordinate (CMC) represents a highly correlated mo
tion of a large ensemble of medium particles, which, as a single varia
ble, undergoes a significant change during a chemical process proceedi
ng in this medium. CMCs naturally arise when charge transfer reactions
in polar solvents are considered. In this context, the most important
problems addressed by the CMC theory are: (1) quantum chemical comput
ations of free energy surfaces explicitly treating a CMC as an essenti
al coordinate, including location of minimum (reactants and products)
and saddle (transition states) points on these surfaces; (2) derivatio
n of stochastic dynamical equations for CMCs and evaluation of their p
arameters, such as masses, friction coefficients, etc.; (3) deduction
of the rate expression for stochastic dynamical systems including CMCs
. These problems are discussed using as examples electron and proton t
ransfer and S(N)2 reactions. Qualitative criterion formulated for when
an explicit consideration of a CMC is absolutely necessary and when i
t can be discarded. (C) 1997 Elsevier Science B.V.