Molecular Models Applied to the Nucleation of Ice

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9307318 Hale In this work, molecular models, effective atom-atom potentials, and Monte Carlo and molecular dynamics computer simulations are used to examine the state, structure, vibrational spectrum, and free energy of formation of small ice/water systems and to develop reliable macroscopic models for the prediction of ice formation rates at low temperatures characteristics of cirrus cloud ice and stratospheric ice. The projects in this proposal are directed at determining the physical characteristics of small ice particles at low temperatures and of small binary water-sulfuric acid clusters. The projects proposed are: (1) a study of "effective surface tensions" for small H2O clusters at low temperatures (-20oC to -80oC); (2) a study of the state (liquid versus solid) and the infrared vibrational spectrum of small H2O clusters at low temperatures; (3) a study of small water-sulfuric acid clusters, with the major emphasis devoted to developing a tractable model for H2O-H2SO4 interactions; and (4) a study of ice formation in four to eight monolayers of H2O on a model substrate. ***