Structure and Dynamics in Highly Excited Molecular States

分子中高激发态的结构和衰变动力学是一个研究领域，为有趣而重要的物理学提供了丰富多样的样本。对诸如光电离、光解离和光缔合等过程的研究需要对分子系统的独特行为方式有更详细和准确的了解。特别是，理解电子和核自旋在分子系统中的作用在几个领域已经变得非常重要，例如，高分辨率光电离研究，化学反应动力学和原子阱中冷分子产生的损失机制。这导致了新的理论努力，将电子和核自旋动力学纳入非常成功的多通道缺陷理论（MQDT）的理论方法。基本的问题被提出，包括：1）如何自旋角动量耦合随能量在分子里德伯态？2)在主量子数和电子角动量的什么值下，不同的物种会出现不同的行为？3)核自旋是否影响里德伯态到不同离子态的电子或转动自电离？4)自旋相互作用在高激发态衰变中电离和解离的相对分支比中起作用吗？5)核间分离在这些自旋动力学中扮演什么角色？本项目拟开始解决这些问题，研究高激发态分子的结构和动力学，包括轨道和转动角动量和振动对分子自旋相互作用的影响，采用时间分辨、共振四波混频光谱的新方法。目标是在给定的里德伯系列或给定的振动级数内进行高能量分辨率的测量，以跟踪角动量耦合作为能量和核间分离的函数的演化。通过研究具有不同分子结构的三个基本系统; H2，N2和OH自由基，可以系统地研究原型相互作用和动力学。这种数据与MQDT分析一起，有望为分子所表现出的独特的核和电子角动量相互作用提供新的见解。

The structure and decay dynamics of highly excited states in molecules is a research area that has provided a rich and diverse sampling of interesting and important physics. Investigations of processes such as photoionization, photodissociation, and photo-association have required more detailed and accurate knowledge of the unique way molecular systems behave. In particular, understanding the role of electronic and nuclear spin in molecular systems has emerged as important in several areas, for example, high resolution photoionization studies, chemical reaction dynamics and loss mechanisms in cold molecule production in atomic traps. This has led to new theoretical efforts to incorporate electronic and nuclear spin dynamics into the highly successful theoretical approach of multichannel defect theory (MQDT). Fundamental questions are being raised, including: 1) How does spin angular momentum coupling vary with energy in molecular Rydberg states? 2) At what values of principal quantum number and electronic angular momentum do different behaviors emerge for different species? 3) Does nuclear spin affect either electronic or rotational autoionization of Rydberg states into different ionic states? 4) Do spin interactions play a role in the relative branching ratio between ionization and dissociation in the decay of highly excited states? 5) What role does internuclear separation play in these spin dynamics? This project proposes to begin addressing these questions by investigating the structure and dynamics of highly excited molecular states, including the effects of orbital and rotational angular momentum and vibration on molecular spin interactions, by using the novel approach of time-resolved, resonant four-wave mixing spectroscopy. The goal is to perform high energy resolution measurements within a given Rydberg series or a given vibrational progression in order to follow the evolution of angular momentum coupling as a function of energy and internuclear separation. By examining three fundamental systems with distinct molecular structures; H2, N2 and the OH radical, prototypical interactions and dynamics can be systematically investigated. This kind of data, taken together with MQDT analyses, promises to provide new insights into the unique nuclear and electronic angular momentum interactions that molecules exhibit.