The Dynamics of Phase Changes in Molecular Clusters

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In this project in the Experimental Physical Chemistry Program of the Chemistry Division, Bartell will study the dynamics of homogeneous nucleation in phase changes in which he will use two new techniques which are relevant to studying solid-state transformations. Experimentally he will probe clusters generated in a supersonic flow using electron diffraction at various times-of-flight to monitor changes in packing during molecular "phase transitions." He will also characterize the molecular behavior computationally using molecular dynamics simulations. The formation of "critical nuclei" will be revealed by the simulations. Many of the same phase transitions will be studied using both techniques. %%% Studies of nucleation, such as the changes from one phase to another in solid- or liquid-state matter, are of crucial importance in many areas of science and technology, such as meteorology, materials engineering, petroleum catalysis, and earth sciences. This research program aims at acquiring a better understanding of such homogeneous phase changes by examining the different ways that molecules are packed in arrays. A special emphasis of this program is a comparison of theoretical prediction and experimental measurement of the rate of phase transitions. New tests of nucleation theory will be made, resulting in insights into the molecular mechanisms of phase changes.