[en] Recent experiments on energy transfer processes in atomic and molecular interactions are described. Of particular interest are the results of studies involving energetically excited atoms. Using laser excitation, collisions between excited sodium atoms were found to form both ionic and highly excited neutral products, neither of which is energetically possible unless both reactant atoms are excited. It is shown that energy from the laser beam is stored in sodium atoms and returned to the system in subsequent collisions between excited species. 15 references