Molecular Spectroscopy to Measure Lifetimes and Collisional Dynamics of Lithium and NaK Molecules

科学家们已经开发出了非凡的方法来研究星际介质中分子的形成，尽管它们距离地球上的实验室有数光年之遥。他们还学会了生成超冷分子，以探索其独特的量子特性。研究小组将使用一种高效的方法，即高分辨率分子光谱和脉冲激光，在热管烤箱中研究目标双原子（2原子）分子，锂和NaK（钠和钾的混合物）的辐射特性。在热管炉中，一些原子通过化学反应结合成分子。当暴露在激光下时，分子从激光中吸收光子，并经历一个跃迁到它们的激发态。被激发的分子最终通过在一个被称为辐射寿命的特征时间尺度上发射光子而返回到较低的量子态。发射光子的衰减时间可以用各种时间分辨光谱技术来探测。研究小组将使用一种复杂的光子计数技术来记录来自特定激发态的单个光子的到达时间。随着这一过程的不断重复，所记录的光子数量不断增加，从而产生分子寿命。此外，研究小组将研究原子和分子碰撞对寿命的影响，因为碰撞经常改变光与分子的相互作用。这项研究的主要潜在好处是获得对分子辐射过程的基本理解，例如，它们发生在星际介质和超冷原子和分子物理学中。该项目还将提供基准值，以测试最近理论寿命计算的可靠性，并促进对原子和分子如何相互作用的理解。该项目的更广泛影响是通过为本科生和研究生提供广泛的实践研究培训，以及开发以研究为基础的教育材料来丰富课程，从而造福社会。学生将获得原子和分子物理学方面的宝贵知识和技能，以及先进的光谱和光学技术。在科学推广项目中，研究团队将与数百名K-12学生及其老师接触，展示光和光学的原理，以促进公众对科学的理解和欣赏。该项目的目标是研究高激发锂和NaK分子的辐射寿命和碰撞动力学。分子跃迁比原子跃迁复杂得多，因为每个分子量子态都由额外的振动和旋转量子能级组成。因此，需要高光谱分辨率来识别正确的转变途径。研究小组将使用非常精确的脉冲激光来启动激发过程，并使用高分辨率分子光谱以及光子计数技术来检测特定振动旋转量子水平的光子。这种研究可以用来检测预解离和辐射结合力，前者是指分子内化学键断裂的过程，后者是指原子碰撞形成新分子的过程。因此，这些测量为寻找在星际云、等离子体物理学和气象学中特别重要的预解离和辐射关联过程开辟了可能性。高激发锂分子的研究特别有趣，因为它在分子状态中具有奇特的双峰结构，在超冷物理中开辟了潜在的应用。这项研究计划的成果将补充最近计算的辐射寿命，并将促进对分子相互作用动力学的理解。锂和NaK分子相对简单但仍然足够丰富的内部结构，是测试自然基本定律和探索量子物质新状态的一个引人注目的目标。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。

Scientists have developed remarkable methods to study the formation of molecules in interstellar medium although they are light years away from the Earth-based labs. They have also learned to generate ultracold molecules to explore their unique quantum properties. The research team will use a highly effective method known as a high-resolution molecular spectroscopy along with pulsed lasers to investigate the radiative properties of target diatomic (2-atom) molecules, lithium and NaK (a mixture of sodium and potassium), in a heatpipe oven. In the heatpipe oven some atoms chemically bind to form molecules. When exposed to laser light, molecules absorb photons from the laser and undergo a transition to their excited quantum state. The excited molecules eventually return to lower quantum states by emitting photons in a characteristic time scale, which is called the radiative lifetime. The decay time of the emitted photons can be probed using various time-resolved spectroscopic techniques. The research team will use a sophisticated photon-counting technique to record arrival time of the individual photon from a specific excited state. As the process repeats, the recorded number of photons builds up and the result yields molecular lifetime. Additionally, the research team will investigate the effect of the atomic and molecular collisions on lifetimes as collisions often alter the interaction of light with molecules. The primary potential benefit of this research is to gain knowledge of the fundamental understanding of radiative processes in molecules as they, for example, occur in the interstellar medium and in ultracold atomic and molecular physics. The project will also provide benchmark values to test the reliability of recent theoretical lifetime calculations and advance the understanding of how atoms and molecules interact. The broader impacts of the project are benefits to society by providing extensive hands-on research training for undergraduate and graduate students, and developing research-based educational materials for curriculum enrichment. Students will gain valuable knowledge and skills in atomic and molecular physics, and in advanced spectroscopic and optical techniques. During the science outreach program, the research team will engage with hundreds of K-12 students and their teachers, demonstrating the principles of light and optics to promote public understanding and appreciation of science.The goal of the project is to study the radiative lifetimes and collisional dynamics of highly excited lithium and NaK molecules. Molecular transitions are much more complex compared to the atomic transitions since each molecular quantum state consists of additional vibrational and rotational quantum levels. Thus, a high spectral resolution is needed to identify the correct transition pathway. The research team will use very precisely pulsed lasers to initiate the excitation process and a high-resolution molecular spectroscopy along with a photon-counting technique to detect photons from a specific vibrational-rotational quantum level. Such study can be used to detect predissociation, which is a process by which a chemical bond within the molecule is broken, and radiative association, which is the formation of a new molecule from colliding atoms. Thus, the measurements open up possibilities for searching predissociation and radiative association processes that are particularly important in interstellar clouds, plasma physics and meteorology. The study of highly excited lithium molecules is specifically interesting due to the exotic double peak structure in molecular states, opening up potential applications in ultracold physics. The output of this research program will be complementary to the recently calculated radiative lifetimes and will advance understanding of molecular interaction dynamics. The relatively simple yet still sufficiently rich internal structure of lithium and NaK molecules is then a compelling target for testing fundamental laws of nature and probing novel states of quantum matter.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.