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 collisional processes 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.
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 molecular beam approaches. Recent investigations on controversy of photochemical processes involved in the formation of ozone hole and the new understanding of basic mechanism involved in the matrix assisted laser desorption ionization method for the analysis of biological molecules will be presented.