The microscopic phenomena which underlie experimental observations for reactivity of solutes dissolved in supercritical fluid solvents are not well understood. There is a wide variety of phenomena which may be implicated including solvent bulk properties, solvent accretion around solute molecules, and preferential clustering of solute molecules around one another. Reaction rates in general depend on both the solute collision frequency and the lifetime of each collision; the microscopic behavior may affect either or both. The engineering design of custom supercritical solvents for a given reaction will not be feasible without a detailed picture of how these effects combine to determine the reaction rate. The PI's plan to attack this problem on two fronts. First, a set of physical experimental studies will be undertaken, investigating both the macroscopic and the microscopic behavior as a function of bulk solvent properties, and utilizing several independent experimental techniques (local dielectric measurement, Heisenberg spin exchange). In concert with the physical measurements, computational experimental studies will be carried out with a view to supplying the experimentally inaccessible portions of the overall molecular picture, again using complementary techniques (Brownian dynamics, molecular dynamics). Each of the approaches will feed the development of the other, leading to an understanding of these systems using the applicable theory.
