High-Resolution Spectroscopy of Heteronuclear Alkali Molecules: Structure and Dynamics

这个项目是一个联合的实验和理论研究计划，解决高分辨率分子光谱学和碰撞动力学领域的重要问题。光谱研究包括测量NaCS和其他异核碱分子的三重态的振动能级，并研究这些能级的精细和超精细结构。我们的目标是绘制势能曲线，研究自旋-轨道和状态之间的非绝热耦合，并利用能级模式，特别是精细和超精细结构中的逐级变化，来推断基本的分子相互作用。通过将数据与理论模型进行比较，我们已经确定了许多重要的动力学效应。特别是，NaK分子表现出幸运的性质组合，使其成为研究分子超精细结构的有趣的“实验室”。例如，我们最近的观察显示，不同的电子态(甚至同一态内不同的动量能级)表现出几种不同的角动量耦合方案，包括纯情况和中间情况。这些精细和超精细结构的水平到水平的变化包含关于电子波函数作为核间分离的函数的微妙变化的信息。已经开发了实验和理论技术来提取这些信息。将进行进一步的高分辨率研究，以探测更接近解离极限的振动能级；在这个范围内的数据将提供有关远程相互作用的信息，并将导致更好地理解当系统从分离的原子过渡到分子区域时电子波函数的微妙变化。我们还将研究NACS，它对冷却和陷阱以及拟议的量子计算方案很感兴趣。这种分子中大的自旋-轨道相互作用导致了强烈的微扰和避免了交叉，为实验和理论提供了有趣的新挑战。我们的程序还研究了各种碰撞过程，包括激发转移、分子取向转移和碰撞中改变原子超精细能级或分子振动能级的速度变化。这样的研究将为原子和分子碰撞理论提供严格的测试。更广泛的影响是，对NaK和NaCS等异核分子的光谱研究引起了广泛的兴趣。具有永久偶极矩的超冷异核碱性硅原子，原则上可以在光学晶格中定向，这表明它在量子计算方案中的应用。Na-Cs和Rb-Cs混合物被用于混合物种的原子陷阱，而分子电子态的知识对于理解光缔合光谱特别感兴趣。对原子和分子碰撞动力学的更好理解将导致在从高温等离子体到超低温区域的广泛环境建模方面的进展。这项工作将有助于教育许多学生。三到四名研究生将根据本提案中描述的项目撰写博士论文。通过利哈伊大学的REU项目，至少有六名本科生将在暑假期间与合作PI一起工作。在过去的25年里，60名本科生与合作的PIS在各种研究项目上进行了合作。这些学生中有一半以上是女性，6名学生属于代表性不足的少数群体；这一模式可能会继续下去。联合PIS将继续派遣研究生和本科生参加APS DAMOP和其他国家会议。

This project is a joint experimental and theoretical research program addressing important questions in the areas of high-resolution molecular spectroscopy and collision dynamics. The spectroscopic studies involve measurements of the ro-vibrational energy levels of triplet states of NaCs, and other heteronuclear alkali molecules, and the investigation of fine and hyperfine structure of these levels. The goal is to map out potential energy curves, study spin-orbit and nonadiabatic coupling between states, and to use the pattern of energy levels, particularly the level-by-level changes in the fine and hyperfine structure, to infer fundamental molecular interactions. By comparing data with theoretical models, we have already identified many important dynamical effects. The NaK molecule, in particular, exhibits a fortunate combination of properties that make it an intriguing "laboratory" for the study of molecular hyperfine structure. For example, our recent observations have revealed that different electronic states (and even different ro-vibrational levels within the same state) exhibit several different angular momentum coupling schemes, including both pure and intermediate cases. These level-to-level variations in the fine and hyperfine structure contain information about subtle changes in the electronic wave functions as a function of internuclear separation. Experimental and theoretical techniques have been developed to extract this information. Further high-resolution studies will be done to probe vibrational levels closer to the dissociation limit; data in this range will provide information about long range interactions and will lead to a better understanding of the delicate changes in the electronic wave function as the system makes the transition from the separated atom to the molecular regime. We will also study NaCs, which is of interest for cooling and trapping and for proposed quantum computing schemes. The large spin-orbit interactions in this molecule, leading to strong perturbations and avoided crossings, provide interesting new challenges for both experiment and theory. Our program also studies a variety of collision processes including excitation transfer, transfer of molecular orientation, and velocity changes in collisions that change atomic hyperfine level or molecular rovibrational level. Such studies will provide stringent tests of atomic and molecular collision theory. Broader impacts are that spectroscopic studies of heteronuclear molecules such as NaK and NaCs are of wide interest. Ultracold heteronuclear alkali diatomics, which have permanent dipole moments, can in principle be oriented in an optical lattice, suggesting applications in quantum computing schemes. Na-Cs and Rb-Cs mixtures are being used in mixed species atom traps, and knowledge of the molecular electronic states is of particular interest for understanding photoassociation spectra. Improved understanding of atomic and molecular collision dynamics will lead to progress in modeling a wide range of environments, from high temperature plasmas to the ultracold regime. The work will contribute to the education of many students. Three or four graduate students will write Ph.D. dissertations based on the projects described in this proposal. At least six undergraduate students will work with the co-PIs during the summers through Lehigh University's REU program. Over the past 25 years, 60 undergraduate students have worked with the co-PIs on various research projects. More than half of these students are female and six belong to underrepresented minority groups; that pattern is likely to continue. The co-PIs will continue to send both graduate and undergraduate students to the APS DAMOP and other national meetings.