The ability to control the evolution of a reaction is a long-standing goal of chemistry. One approach is to use the electric field provided by a laser pulse as the guide. Recent work has focused on shaping and timing the pulse so that the field interacts with the molecules in a particular way to influence the energy flow through the molecule and thus eventually the course of a reaction. The optimal pulse shape is achieved by using a feedback loop , focusing on a signal related to the desired outcome and allowing a computer algorithm to change the pulse shape during repeated cycles of the experiment until the signal is maximised. This optimal control scheme has proved to be able to control a wide range of chemical systems, but the complicated pulse shapes provide little insight into the procedure, and the experiments have a black box nature. A different, very appealing, approach to control through a laser field is to use the field to change the shape of the potential energy surface over which the reaction proceeds. This can be acheived using a strong pulse which induces Stark shifting of the surface. By careful timing of a pulse of the appropriate strength, it has been shown that it is possible to control the products from IBr dissociation by effectively changing the barrier height to the different possible channels.The project aims to investigate theoretically this potentially general approach to laser control. The results should start to build up a picture of how the complicated potential energy surfaces of small molecules are altered by interaction with the field. This will help in the development of experiments and in our understanding of how molecules behave in a light field.