Ultrafast detection and control of molecular dynamics

Many elementary chemical and physical processes such as the breaking of a c hemical bond or the vibrational motion of atoms within a molecule take plac e on a femtosecond (fs = 10(-15) s) or picosecond (ps = 10(-12) s) time sca le. It is now possible to monitor these events as a function of time with t emporal resolution well below 100 fs. This capability is based on the pump- probe technique where one optical pulse triggers a reaction and a second de layed optical pulse probes the changes that ensue. To illustrate this capab ility, the dynamics of ligand motion within a protein are presented. Moving beyond casual observation of a reaction to active control of its outcome r equires additional experimental and theoretical effort. To illustrate the c oncept of control, the effect of optical pulse duration on the vibrational dynamics of a tri-atomic molecule are discussed. The experimental and theor etical resources currently available are poised to make the dream of reacti on control a reality for certain molecular systems.