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 transforms reactant molecules into product molecules. Unfortunately it is not possible to see individual atoms and molecules with our naked eyes. However, recent advances in experimental methods, have made it possible to "visualize" the exact details of how chemical reactions taking place.
Whether two reactant molecules can transform into product molecules during collision processes depend 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 one energizes a molecule, there are many different modes in which we can deposit the energy required. Whether the energy is in the translational, the rotational, the vibrational, or the electronic degrees of freedom will have effects in promoting chemical reactions. With the advancement of various laser techniques, it has now become possible to energize atoms and molecules quite effectively through laser excitation. It has also become possible to control the alignment of electronically excited atomic orbital by using polarized laser.
In this lecture, exciting field of chemical reaction dynamics using molecular beam and laser techniques will be introduced, and the implication of these studies to the understanding of macroscopic chemical phenomena will be discussed. |
