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已经完全为人所知，困难只在于这些定律的应用会导致过于复杂而无法求解的方程。”我们将表明，最近发展的量子动力学方法现在可以克服狄拉克注意到的困难。当前项目的基本成果将是表明，一个中等复杂的多原子分子的动力学现在可以完全在量子运动的基础上描述，尽管在几百飞秒的非常短的时间尺度上。最近发展的量子直接动力学方法在完全量子水平上处理分子的所有电子和原子核，将用于模拟紫外光子吸收后分子的运动。在超快时间尺度上，这种运动总是揭示出大量的量子现象，如电子非绝热过程（即电子形成化学键重新排列时电子状态的变化）和隧道效应。在实践方面，该项目将侧重于三种类型的实验。首先，将模拟氢在气相中从小杂芳分子上的光分离。在这些实验中，光子对分子的初始激发引发化学反应，并导致氢的解离，氢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。其次，开发了新的泵浦探针实验，以飞秒时间分辨率研究溶液中的类似反应。这些实验提供了时间分辨光谱图像的化学反应，允许重建动力学和看到他们的机制。第三，随着斯坦福大学和汉堡新的国际自由电子激光x射线设备的建设，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射线探针脉冲与飞秒激光脉冲在可见光和紫外区结合，引发化学反应，然后通过测量x射线衍射图像的变化来进行化学动力学。在上述实验中研究的分子通常代表了更大的生物重要分子物种的原型或构建块，它们的光动力学通常模拟了在光的影响下发生的生物体过程。提出的理论将解释实验，并有助于揭示超快化学的新机制。另一方面，全量子理论将以实验为基准，并将证明狄拉克指出的困难现在是可以克服的。

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.