Introduction: Femtochemistry

Only a few years after femtochemistry was first established as a field of research did we witness an explosion of research in all phases of matter and in biological systems. The reason behind this explosion is fundamentals-chemical bonds form and break on the femtosecond time scale, and on this scale of time we can freeze the transition states at configurations never seen before. Even if there is no reactants-to-products transformations - physical changes - one is observing the most elementary of all molecular processes. On a time scale shorter than the vibrational and rotational periods, the ensemble behaves coherently as a single-molecule trajectory.