Excited State Dynamics

该程序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子的吸收作出反应，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。我们的方法利用轨迹模拟，其中分子的原子和电子自由度的时间演化是通过使用从头算电子结构方法“在飞行中”计算势能面来确定的。然而，分子轨迹不是可观察的量；这就要求使用超快激光脉冲探测分子波包。高水平模拟预测时间分辨光谱的能力将理论和实验方法结合起来，揭示了超快现象的机理细节。我们的团队在学术超快激光实验室和先进的光源设施中与广泛的实验合作者合作，研究在固有时间尺度上询问分子运动的新方法。***目前的提案将雇用四名NSERC支持的学生进行三个主要研究重点：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“完全模拟”，以及3)研究分子动力学的新型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理解中的持续差距：缺乏激发态过程的描述性理论和模型。在特定选择的分子示例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（锥形）交叉电子表面的控制动力学的规则。第二个要点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对实验观测结果的直接模拟。我们的团队在我们开发的模拟工具包和我们雇用的实验合作者网络中都具有独特的定位，可以展示理论方法与现代超快实验的能力。最后，光源的发展现在允许飞秒x射线脉冲，可以在超快泵浦探针实验中部署。x射线光子的波长是原子间距离的数量级，有望获得分子中特定原子位置的电子环境的特定位置信息。我们的目标是用我们定位良好的技术来指导对这些新实验的解释。该项目将为学生提供在全球理论和实验合作伙伴网络中进行前沿、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.**