Excited State Dynamics

该计划采用计算量子化学方法，不仅揭示了分子如何在飞秒时间尺度上对光光子的吸收做出反应，而且还揭示了如何使用时间分辨光谱技术观察这种动态响应。 我们的方法利用轨道模拟，其中的原子和电子的分子的自由度的时间演化是通过计算势能面的“上的飞行”，使用从头计算电子结构方法。 然而，分子轨迹是不可观测的量;这需要使用超快激光脉冲探测分子波包。 高级模拟预测所产生的时间分辨光谱的能力将理论和实验方法结合起来，以揭示超快现象的机制细节。 我们的团队与学术超快激光实验室和先进光源设施的广泛实验合作者网络合作，研究在固有时间尺度上询问分子运动的新方法。目前的建议将雇用总共四个NSERC支持的学生在三个主要的研究方向：1）分子激发态动力学模型理论的发展，2）时间分辨光谱实验的“完整模拟”，和3）调查分子动力学的新型X射线探针的潜力。 第一个研究重点解决了我们对激发态过程的理解中存在的一个持续的差距：缺乏激发态过程的描述性理论和模型。 在特定的分子例子和模型系统上运行我们的“模拟机器”的最终目标是构建涉及（圆锥形）相交电子表面的动力学规则。第二个推力认识到，动力学方法的验证需要与实验结果进行比较。最明确的比较是通过直接模拟实验观测。无论是在我们开发的模拟工具包中，还是在我们雇用的实验合作者网络中，我们的团队都处于独特的地位，以展示理论方法与现代超快实验对话的能力。 最后，光源的发展现在允许飞秒X射线脉冲，可以部署在超快泵浦探测实验中。X射线光子的波长是原子间距离的数量级，并且有望产生关于分子中特定原子位置处的电子环境的位置特定信息。 我们的目标是使用我们的定位技术来指导这些新实验的解释。该计划将为学生提供在全球理论和实验合作者网络中进行前沿，多学科研究的机会。

This program employs computational quantum chemical methods to reveal not only how molecules respond on femtosecond timescales to the absorption of a photon of light, but also how this dynamical response may be observed using time-resolved spectroscopic techniques.  Our approach utilizes trajectory simulations in which the time-evolution of the atomic and electronic degrees of freedom of molecules are determined by computing potential energy surfaces 'on-the-fly' using ab initio electronic structure methods.  However, molecular trajectories are not observable quantities; this requires that the molecular wave packet be probed using ultrafast laser pulses.  The ability of high-level simulation to predict the resulting time-resolved spectra unifies theoretical and experiment approaches to unravel the mechanistic details of ultrafast phenomena.  Our group is engaged with a wide network of experimental collaborators, in both academic ultrafast laser labs and advanced light source facilities, to investigate novel methods of interrogating molecular motions on inherent timescales.***The current proposal will employ a total of four NSERC supported students in three main research thrusts: 1) the development of model theories for molecular excited state dynamics, 2) the 'complete simulation' of time-resolved spectroscopic experiments, and 3) investigation of the potential for novel X-ray probes of molecular dynamics.  The first research thrust addresses a persistent gap in our understanding of excited state processes: the lack of descriptive theories and models for excited state processes.  The ultimate goal of running our "simulation machinery" on specifically chosen molecular examples and model systems is the construction of rules governing dynamics involving (conically) intersecting electronic surfaces. The second thrust recognizes that validation of dynamical methods require comparison to experimental results. The most unambiguous comparison to be made is via the direct simulation of experimental observables. Our group is uniquely positioned, both in the simulation toolkit we've developed and in the network of experimental collaborators we employ, to demonstrate the ability of theoretical methods to speak to modern ultrafast experiments.  Lastly, developments in light sources now allow for femtosecond X-ray pulses that may be deployed in ultrafast pump-probe experiments. The wavelengths of X-ray photons is on the order of interatomic distances and promise to yield location specific information on the electronic environment at particular atomic sites in a molecule.  Our aim is to guide the interpretation of these new experiments using our well-positioned techniques. This program will provide students with an opportunity to conduct leading-edge, multidisciplenary research within a global network of theoretical and experimental collaborators.**