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Yuan-Tseh Lee 
2009-06-30 
10:30 - 11:30
101 , Mathematics Research Center Building (ori. New Math. Bldg.)

Every macroscopic chemical transformation, whether it is atmospheric ozone depletion or the burning of a candle, consists of millions of microscopic chemical events which involve collisions between molecules. It has been the dream of scientists for a long time to observe and understand the details of molecular collisions which transform reactant molecules into product molecules with our naked eyes. During the last several decades, because of the advances in crossed molecular beams method and laser technology, especially, from the measurements of product angular and velocity distributions, it has become possible to “visualize” exact details of how chemical reactions take place through molecular collisions or through photochemical processes. Whether two reactant molecules can transform into product molecules during collisional processes depends not only on the orientations of molecules when they approach each other, but also on the energy contents of reactant molecules. Reactants must contain sufficient energy to overcome potential energy barriers on their way to product formation. However, when a molecule is energized, there are many different modes in which the required energy could be deposited. Whether the energy is in the translational, the rotational, the vibrational, or the electronic degrees of freedom will have different effects in promoting chemical reactions. Very often reactions might also proceed with different mechanism. With the advancement of various laser techniques, it has now become possible to energize atoms and molecules quite effectively through laser excitation. In this lecture, in addition to illustrate experimental details of crossed molecular beams method, examples will be given to demonstrate how detail information on the dynamics of chemical reactions and photochemical processes can be obtained using various experimental approaches.