Stereodynamic Control of Cold Molecular Collisions

长期以来，化学家们一直试图控制化学反应的结果。这种控制需要在分子水平上了解潜在的机制和反应途径。控制化学反应和分子碰撞结果的一种方法是通过立体动力学，即控制它们相互接近时的相对方向和排列。这种控制在接近开尔文或低于开尔文的温度下更为有效，因为在这种温度下，由于物质的波动行为，量子效应变得显著。这种分子相互作用的控制对于量子信息处理和量子计算等新兴量子技术至关重要，这些技术在受控环境中使用冷和超冷分子，其相互作用由外部场操纵。提出的研究探索如何通过立体动力学控制分子相互作用，以及如何将这种控制扩展到化学反应，从而使使用冷捕获分子的新兴量子技术受益。这项工作超越了学科界限，作为这项研究的一部分而开发的计算算法适用于化学、物理和天体物理学等不同领域的分子过程。冷分子和超冷分子正迅速成为分子碰撞和化学反应控制研究的新范例。在选定的运动、内部和方向量子状态下创建它们的能力允许在深度量子状态下进行“按需化学”实验，其中反应结果受到外场、几何相位和量子干涉效应的强烈影响。新技术，如在超音速分子束中碰撞物质的共膨胀（束内散射）与stark诱导的绝热拉曼通道（SARP）相结合，允许H2和HD等分子最初在特定或磁投影量子数的相干叠加中制备的冷立体化学，开辟了一个全新的冷控制化学体系，而无需使用外部捕获场。由于实验缺乏能量分辨率，明确计算能量分辨散射振幅对于提供碰撞动力学的机制见解至关重要。提出的研究包括全六维的HCl+HD和CO+HD碰撞，以及使用SARP方法制备的振动和旋转激发分子的原子-分子化学反应。所提出的研究可能还揭示了立体动力学制备和非绝热量子干涉效应如何影响冷和超冷碰撞中的反应性。该项目将培养一名博士后，为传统上代表性不足的社区的学生提供从事STEM相关研究的机会，并为未来的劳动力发展做出贡献。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。

Chemists have long sought to control the outcome of chemical reactions. This control requires a molecular level understanding of the underlying mechanisms and reaction pathways. One approach to control the outcome of chemical reactions and molecular collisions is through stereodynamics, i.e., controlling their relative orientations and alignments as they approach each other. This control is even more effective at temperatures close to a kelvin and below where quantum effects become significant due to the wave behavior of matter. Such control of molecular interactions is paramount to emerging quantum technologies such as quantum information processing and quantum computing that use cold and ultracold molecules in controlled environments and whose interactions are manipulated by external fields. The proposed research explores how molecular interactions can be controlled through stereodynamics and how such control can be extended to chemical reactions, thus benefitting emerging quantum technologies that use cold trapped molecules. This work transcends disciplinary boundaries and the computational algorithms developed as part of this research are applicable to molecular processes in diverse areas of chemistry, physics, and astrophysics. Cold and ultracold molecules are rapidly emerging as new paradigm for controlled studies of molecular collisions and chemical reactions. The ability to create them in selected motional, internal and orientational quantum states allows “chemistry-on-demand” experiments in the deep quantum regime where the reaction outcomes are strongly influenced by external fields, geometric phase, and quantum interference effects. Novel techniques such as co-expansion of the colliding species in a supersonic molecular beam (intra-beam scattering) combined with the Stark-induced adiabatic Raman Passage (SARP) allow cold stereochemistry with molecules like H2 and HD initially prepared in a specific or a coherent superposition of magnetic projection quantum numbers, opening up an entirely new regime of cold controlled chemistry without using external trapping fields. Since the experiments lack energy resolution, explicit calculations of energy resolved scattering amplitudes are crucial to provide mechanistic insights into the collision dynamics. The proposed studies include HCl+HD and CO+HD collisions in full six-dimensions and atom-molecule chemical reactions with vibrationally and rotationally excited molecules prepared using the SARP method. The proposed studies may additionally reveal how stereodynamic preparation and non-adiabatic quantum interference effects influence reactivity in cold and ultracold collisions. The project will train a postdoc, provide opportunities for students from traditionally underrepresented communities to engage in STEM related research, and contribute to future workforce development.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.