Stark shifting the barrier to reaction: Control through using a strong laser field to shape the potential energy surfaces

能够控制反应的演变是化学的长期目标。一种方法是利用激光脉冲提供的电场作为导向。最近的工作集中在脉冲的形状和定时上，这样电场就能以一种特殊的方式与分子相互作用，从而影响通过分子的能量流，从而最终影响反应的过程。最佳脉冲形状是通过使用反馈回路来实现的，聚焦于与期望结果相关的信号，并允许计算机算法在重复的实验周期中改变脉冲形状，直到信号最大化。这种最优控制方案已被证明能够控制广泛的化学系统，但复杂的脉冲形状提供了很少的洞察程序，并且实验具有黑箱性质。一个不同的，非常吸引人的，通过激光场控制的方法是利用激光场来改变反应进行的势能面形状。这可以通过一个强脉冲来实现，它可以引起表面的斯塔克位移。通过适当强度的脉冲定时，已经表明，通过有效地改变不同可能通道的势垒高度来控制IBr解离产物是可能的。该项目旨在从理论上研究这种潜在的通用激光控制方法。结果应该开始建立一个小分子复杂的势能表面是如何通过与场的相互作用而改变的图像。这将有助于实验的发展和我们对分子在光场中的行为的理解。

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.