Laser Control of Quantum Evolution in Molecules

分子内的电子和质子在受到强力作用时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很重要：例如，质子运动在有机化学、能量储存和生物医学中做了很多工作，因此利用外力控制质子运动在未来的化学合成或量子计算中可能是有用的，甚至可以用来分解水来制造氢燃料。这项NSF计划将探索在实验室中使用外部激光场来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，以克服将分子聚集在一起的内部场，大约是每埃斯特罗姆的伏特；它们必须能够以不到万亿分之一秒的速度进行脉冲开关，以跟上分子内部的自然运动速度。使用这些激光工具的研究将测试分子转化的基本模型，例如推测存在特殊的原子几何结构，其中分子变得特别容易受到外力的控制。要测试的分子是水和乙炔，这两个分子都是许多化学过程中富含质子的构件。这项研究还将为学生和博士后提供培训，从而为他们在下个世纪贡献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、能量生产等许多重要物理和化学过程的关键。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。这些路径之所以复杂，部分原因是分子中每个原子的运动通常会影响到其他每个原子。其结果是，运动发生在一个高维空间：像水这样一个简单的三原子分子有三个内部维度；但分子中每增加一个原子，就有三个额外维度。这个空间的高维拓扑很难想象，也很不直观。它导致了这个分子景观中的特殊位置--嵌入在更高维空间的接缝或表面结构--在那里原子间的键可以重新排列，而不会造成任何能量损失。这里的目的是了解强激光场如何改变耦合原子运动中的高维特征，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。这验证了一种假设，即外部强场与原子运动耦合可以控制和重定向这些自然过程。水和乙炔之所以被选为研究对象，是因为它们的内部运动由氢原子主导，而氢原子的运动速度更快，因为它们的质子核质量较低。这增强了正在研究的效果。这些研究使用红外、紫外线和真空紫外相干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，要么让分子分崩离析，要么通过激光产生的库仑爆炸迫使它们分开。了解分子在外部领域的行为与许多实际应用领域相关，包括催化、质子医学治疗和光引发氢酶化学。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.