An exact theory of friction for reactive collisions in a solvent using an interaction representation

An exact (classical) mechanical theory of reactive collisions in a solvent is developed and applied. In the theory the motion of the solvent including its interaction with the solute is treated mechanically and without approximation. Yet equations of motion which formally invoke only the coordinates of the solute can be written down and solved. A computational example, a Cl+Cl₂ collision in liquid Ar, is used to illustrate the formal results. The exact equations of motion for the solute degrees of freedom can be interpreted as a motion on the potential for the free reactants (as in the gas phase) subject however to friction. These equations are derived using an interaction picture. Their numerical solution, which is possible and is illustrated by an example, is equivalent to performing a full, exact, molecular dynamics simulation. The feasibility of approximate solutions of the equations, which retain the essential physics, is considered.