Laser Control of Quantum Evolution in Molecules

当电子和质子在分子内受到强作用力时，它们的运动是分子和化学科学中的一个基本问题。理解和控制这种内部运动是很重要的：例如，质子运动在有机化学，能量存储和生物医学中做了很多工作，因此用外力控制质子运动可能在未来的化学合成或量子计算实现中有用；甚至可以分解水来制造氢燃料。这个NSF项目将探索在实验室中利用外部激光场创造和控制分子内质子和电子运动的新方法。激光场强必须足够大，以克服使分子结合在一起的内部场，达到每埃伏特的数量级；它们还必须能够在远低于万亿分之一秒的时间内开启和关闭脉冲，以跟上分子内部运动的自然速度。使用这些激光工具进行的研究将测试分子转化的基本模型，例如存在特殊的原子几何形状，其中分子特别容易受到外力的控制。要测试的分子是水和乙炔，它们都是许多化学过程中富含质子的基石。这项研究还将为学生和博士后提供培训，从而为他们在未来一个世纪支持国家经济和安全所需的技术人才做好准备。分子内运动是分子物理学的核心问题之一，是化学合成、能量产生等许多重要物理化学过程的关键。这项活动探索了超快激光诱导的强场相互作用如何改变分子中原子的运动，从而改变化学变化的路径。这些路径很复杂，部分原因是分子中每个原子的运动通常会影响到其他原子。结果是运动发生在高维空间中：像水这样简单的三原子分子有三个内部维度；但是分子中每增加一个原子就会增加三个维度。这个空间的高维拓扑结构很难可视化，非常不直观。它导致了分子景观中的特殊位置——嵌入在高维空间中的接缝或表面结构——在那里原子间键可以重新排列而不会产生任何能量损失。这里的目标是了解耦合原子运动中的高维特征如何被强激光场改变，以增强、抑制或修改原子重排、快速电离、多重电离，甚至库仑爆炸。这验证了一个假设，即与原子运动耦合的外部强场可以控制和重定向这些自然过程。之所以选择水和乙炔作为研究对象，是因为它们的内部运动是由氢原子主导的，而氢原子由于质子核的质量较低而运动得更快。这增强了研究中的效果。研究使用红外、紫外和真空紫外相干激光场来激发和控制这些分子系统。激发和控制的结果是通过直接记录所有分子成分的速度来测量的，要么让分子分裂，要么用激光产生的库仑爆炸迫使它们分开。了解分子在外场中的行为与许多实际应用领域相关，包括催化、质子医学治疗和光启动氢化酶化学。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The motion of electrons and protons inside molecules when they are subjected to strong forces is a fundamental issue in molecular and chemical science. Understanding and controlling this internal motion is important: For example, proton motion does much of the work in organic chemistry, energy storage, and biomedicine, therefore controlling proton motion with external forces may be useful in future implementations of chemical synthesis or quantum computing; or even for splitting water to make hydrogen fuel. This NSF program will explore new ways to create and control the motion of protons and electrons inside molecules using external laser fields in the laboratory. The laser field strengths must be large enough to overcome the internal fields that hold molecules together, on the order of volts per Angstrom; and they must be able to pulse on and off in well under a hundredth of a trillionth of a second as well, to keep up with the natural pace of movement inside molecules. Research using these laser tools will test basic models of molecular transformations, such as conjectures that there are special atomic geometries where molecules become especially susceptible to control by outside forces. The molecules to be tested are water and acetylene, both proton-rich building-blocks for many chemical processes. This research will also provide training for students and postdocs, and thus prepare them to contribute technical talents that are needed to support the nation's economy and security in the coming century. Intramolecular motion is one of the core issues in molecular physics, and the key to many important physical and chemical processes such as chemical synthesis and energy production. This activity explores how ultrafast laser-induced strong field interactions can change the motion of atoms in molecules and therefore alter the path of chemical change. These paths are complicated in part because the motion of every atom in a molecule generally affects every other atom. The result is that motion takes place in a high-dimensional space: three internal dimensions for a simple three-atom molecule like water; but three additional dimensions for every additional atom in the molecule. The high-dimensional topology of this space is difficult to visualize and highly non-intuitive. It leads to special locations in this molecular landscape -- seams or surfaces structures embedded in the higher dimensional space -- where the interatomic bonds can rearrange without any energy penalty. Here the objective is to understand how high-dimensional features in coupled atomic motion can be altered by strong laser fields to enhance, suppress, or modify atomic rearrangement, rapid ionization, multiple ionization, and even Coulomb explosions. This tests a hypothesis that external strong fields coupled to atomic motion can control and redirect these natural processes. Water and acetylene have been selected for study because their internal motion is dominated by hydrogen atoms, which move more rapidly because of the low mass of their proton nuclei. This enhances the effects under study. The investigations use infrared, ultraviolet, and vacuum ultraviolet coherent laser fields to both excite and control these molecular systems. Results of the excitation and the control are measured by recording the velocities of all of the molecular constituents directly, either by allowing the molecules to fall apart or by forcing them apart with a laser-produced Coulomb explosion. Understanding molecular behavior in external fields has relevance for many practical applications areas, including catalysis, proton medical therapy and photo-initiated hydrogenase chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.