A fully quantum theory of ultrafast chemical dynamics.

1929年，狄拉克说：“对大部分物理学和整个化学进行数学处理所必需的基本定律因此是完全已知的，困难只在于应用这些定律会导致方程过于复杂而无法求解。“我们将证明，最近开发的量子动力学方法现在可以克服狄拉克注意到的困难。目前项目的基本成果将表明，一个适度复杂的多原子分子的动力学现在可以完全基于量子运动的基础上进行描述，尽管时间尺度很短，只有几百飞秒。最近发展起来的量子直接动力学方法将在完全量子水平上处理分子的所有电子和原子核，该方法将用于模拟分子在吸收UV光子后的运动。在超快时间尺度上，这种运动总是揭示了大量的量子现象，如电子非绝热过程（即当形成化学键的电子重新排列时电子状态的变化）和隧道效应。在实践方面，该项目将侧重于3种类型的实验。 首先，我们将模拟氢气从芳香杂环小分子上的光解离.在这些实验中，光子对分子的初始激发引发了化学反应，并导致氢的解离，随后在几十飞秒的时间延迟下电离，并检测到反应的“离子图像”。这允许通过分析其产物的空间和能量分布的演变来获得关于反应动力学的非常详细的信息。 第二，新的泵浦探测实验已经发展到飞秒时间分辨率的溶液中研究类似的反应。这些实验提供了化学反应的时间分辨光谱图像，可以重建动力学并了解其机制。 第三，随着在斯坦福大学和汉堡建造新的国际自由电子激光X射线设施，新的和独特的实验正在成为可能。在新的时间分辨X射线衍射实验中，X射线探测脉冲与可见光和紫外光区域的飞秒激光脉冲相结合，引发化学反应，并通过测量X射线衍射图像的变化来跟踪化学动力学。 在上述实验中研究的分子通常代表较大的生物学重要分子物种的原型或构建块，并且它们的光动力学通常模拟在光的影响下发生的活生物体中的过程。提出的理论将解释实验，并将有助于揭示超快化学的新机制。另一方面，完全量子理论将以实验为基准，并将表明狄拉克所指出的困难现在可以克服。

In 1929 Dirac stated that: "The fundamental laws necessary for the mathematical treatment of a large part of physics and the whole of chemistry are thus completely known, and the difficulty lies only in the fact that application of these laws leads to equations that are too complex to be solved." We will show that recently developed methods of quantum dynamics can now overcome the difficulty noticed by Dirac. The fundamental outcome of the current project will be to show that the dynamics of a moderately complicated polyatomic molecule can now be described solely on the basis of quantum lows of motion albeit on a very short time scale of few hundred femtoseconds. Recently developed methods of Quantum Direct Dynamics which treat all electrons and nuclei of a molecule on a fully quantum level will be used to simulate the movements of molecules which follow the absorption of a UV photon. On the ultrafast time scale this motion always reveals a wealth of quantum phenomena such as electronically nonadiabatic processes (i.e. the changes in electronic states when electrons forming chemical bonds rearrange) and tunnelling. On the practical side the project will focus on 3 types of experiments. First, hydrogen photo- detachment from small heteroaromatic molecules studied in the gas phase will be simulated. In these experiments the initial excitation of a molecule by a photon initiates chemistry and causes the dissociation of hydrogen, which is later ionised with time delay of a few tens of femtoseconds and the "ion image" of the reaction is detected. This allows to obtain very detailed information about the dynamics of reaction by analysing the evolution of spatial and energy distribution of its products. Second, the new pump-probe experiments have been developed to study similar reactions in solution with femtosecond time resolution. These experiments provide time resolved spectral images of chemical reactions which allow to reconstruct the dynamics and to see their mechanisms. Third, new and unique experiments are becoming possible now with the construction of the new international Free Electron Laser X-ray facilities in Stanford and Hamburg. In the new time resolved X-ray diffraction experiment, an X-ray probe pulse is combined with femtosecond laser pulses in the visible and UV region, which initiate chemistry, and chemical dynamics is followed by measuring the changes in the X-ray diffraction images. The molecules studied in the above experiments often represent prototypes or building blocks of larger biologically important molecular species and their photodynamics often models the processes in living organisms, which occur under the influence of light. The proposed theory will explain the experiments and will help to unravel new mechanisms of the ultrafast chemistry. On the other hand the fully quantum theory will be benchmarked against experiment and it will be shown that the difficulty pointed out by Dirac can now be overcome.