Probing intramolecular dynamical processes in electronically excited states of small aromatic molecules

一个分子可以看作是球和弹簧的集合。如果分子某一部分的弹簧被扭曲，能量就会转移到分子的其他部分。化学家们对这种转移过程的机理和时间尺度很感兴趣，因为它决定了分子可以经历的各种反应。在这里提出的实验中，这种调整将来自具有明确能量的非常短的激光脉冲。这个能量将与分子中的共振相匹配。分子周围能量的转移将由第二个激光脉冲监测，该激光脉冲相对于第一个脉冲将被延迟，以便它到达一个明确的时间，不到十亿分之一秒。第二个激光脉冲将导致一个电子从分子中射出，其行为作为控制时间延迟的函数，将使我们能够观察到能量在分子框架周围移动。我们选择了一组分子进行研究，这些分子都是基于环结构的，环上附着着各种相关的原子群。这将使我们能够以系统的方式检查改变分子结构的影响。因此，我们希望找到共同的线索，使我们能够理解分子中的能量传递过程。

A molecule can be considered as a collection of balls and springs. If a spring in one part of a molecule is tweaked, the energy can be transferred to other parts of the molecules. Chemists are interested in the mechanism and the timescale of this transfer process because it dictates the kinds of reactions that the molecule can undergo. In the experiments proposed here, the tweak will come from a very short laser pulse that has a well-defined energy. This energy will be matched to a resonance in the molecule. The transfer of the energy around the molecule will be monitored by a second laser pulse which will be delayed with respect to the first so that it arrives at a well-defined time, less than one ten billionth of a second later. The second laser pulse will cause the ejection of an electron from the molecule whose behaviour as a function of the controlled time delay will enable us to watch the energy moving around the molecular framework. We have chosen a set of molecules for study which are all based on a ring structure, with various related groups of atoms attached to the rings. This will enable us to examine in a systematic way the effect of changing the molecular structure. Thus, we hope to find common threads that will enable us to understand energy transfer processes in molecules.