Optimal control theory is applied to prepare excited state wave packets localized in specific regions of a reaction surface which can be used as a sensitive tool to clarify and manipulate characteristic reaction features. In the present example of the Na-H-2 collision complex this allows us to study the quantum dynamics in the vicinity of a conical intersection and the population transfer through it in great detail. We could clarify the relaxation mechanism and extract the vibrational distribution of the H-2 fragment resulting after the collision. Employing differently shaped laser pulses the ability to control reactions through conical intersections is proven. (C) 2003 American Institute of Physics.