Publisher Summary Major advances in laser technology over the last fifteen years have resulted in lasers, which can operate on the femtosecond scale. By bringing the pulse time down to significantly less than the time taken for many chemical reactions, these ultrafast lasers have allowed an unprecedented ability to probe inside a chemical reaction as it is taking place. These new techniques have resulted in a greatly increased understanding of the dynamics and mechanisms of elementary chemical reactions. One such technique, that of pump-probe experiments has allowed the observation of the formation and evolution of several transition states. This ability has naturally led to the quest to control the reaction with laser pulses. To this end, different control schemes have been proposed. Due to its relative simplicity, the isolated NaI molecule has been studied extensively with pump-probe techniques both experimentally, and theoretically. This chapter investigates theoretically the femtosecond pump-probe ionization of NaI and CsI when aggregated with a molecule of acetonitrile CH3CN.