Non-Adiabatic Photonic Processes in Molecular Plasma

当光在分子气体（如空气）中传播时，它可以从分子中除去电子，这一过程被称为光电离。这个过程和与之相反的过程，即重组，在现代技术、大气科学、天体物理学和许多其他研究领域中起着极其重要的作用。这就是为什么越来越需要能够解释和预测电离辐射下分子气体行为的理论方法的原因。虽然在原子光离的理论描述方面取得了重大进展，但分子气体的理论情况远非令人满意。由于分子的复杂量子力学结构，对分子气体中电离的可靠理论描述是复杂的。本项目的主要科学问题是理论能否描述双原子分子的光电离，例如空气中的双原子分子，特别是在没有实验数据的情况下。该项目的主要目标是开发能够模拟线性分子（和带负电荷的分子离子）光电离的理论方法。所提出的研究的一个重要的更广泛的影响是基于网络的平台和相关方法的发展，以在工作室模式的课堂上教授量子力学。该平台允许学生和他们的导师对量子力学的所有主要概念进行数值实验。分子氮N2的光电离谱，将计算光子能量高于电离阈值从基态的振动。计算N2+的基电子态和N2+的三个最低电子态之间的跃迁偶极矩函数，并提供给学界。将考虑N2和N2+的振动和旋转运动，以及N2+离子电子态之间的非绝热耦合。为此，将采用多通道量子缺陷理论（MQDT）和振动框架变换。利用已建立的N2光离理论模型，将研究在几个实验组中观察到的N2+的无腔激光。该项目的第二个目标是研究光分离的时间延迟和阈值规律。PI将模拟和研究分子阴离子的光剥离光谱，考虑到非绝热效应，光电子与分子旋转和振动运动的相互作用。该研究将包括光谱中的主要特征（如共振、阈值行为……）对分子偶极矩、分子的旋转和振动结构以及一个或几个偶极电子态的存在的依赖。该研究将使用FEM（有限元法）代码进行，该代码能够处理电子与线性分子的碰撞，同时解决电子和目标的旋转振动运动的薛定谔方程。本文将考虑光剥离过程中的时间延迟，并提出一种在光剥离实验中观察时间延迟的方案。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。

When light propagates through a gas of molecules, such as air, it can remove electrons from the molecules, the processes known as photoionization. This process and the one reverse to it, recombination, play an extremely important role in modern technology, in atmospheric sciences, in astrophysics, and many other fields of research. This is the reason why there is a growing need for theoretical methods able to interpret and predict behavior of molecular gases under ionizing radiation. Although there has been significant progress in a theoretical description of atomic photoionization, the situation with theory in molecular gases is far from being satisfactory. A reliable theoretical description of ionization in molecular gases is complicated due to the complex quantum-mechanical structure of molecules. The main science question of the present project is whether theory can describe photoionization of diatomic molecules, such as those present in air, especially in situations where experimental data do not exist. The major goal of the project is to develop theoretical methods able to model photoionization of linear molecules (and negatively charged molecular ions). An important broader impact of the proposed research is the development of a web-based platform and a related methodology to teach Quantum Mechanics in studio mode-like classes. The platform allows students and their instructors to perform numerical experiments for all main concepts of Quantum Mechanics.The photoionization spectrum of molecular nitrogen, N2, will be computed for photon energies above the ionization threshold from the ground vibronic state. Transition dipole moment functions between the N2 ground electronic state and three lowest electronic states of N2+ will be computed and made available to the community. Vibrational and rotation motion of N2 and N2+ will be accounted for as well as non-adiabatic coupling between electronic states of the N2+ ion. For this purpose, the multichannel quantum defect theory (MQDT) and rovibronic frame transformation will be employed. Using the developed theoretical model of photoionization in N2, cavity-free lasing of N2+, observed in several experimental groups, will be studied. The second objective of the project is to study time-delay and thresholds laws in photodetachment. The PI will model and study photodetachment spectra of molecular anions, taking into account non-adiabatic effects, interaction of the photoelectron with rotational and vibrational motion of the molecule. The study will include the dependence of main features in the spectra (such as resonances, threshold behavior...) on the dipole moment of the molecule, the rotational and vibrational structure of the molecule, and the presence of one or several dipolar electronic states. The study will be performed using a FEM (Finite-element method) code able to treat collisions of electrons with linear molecules, solving the Schrodinger equation for electronic and rovibrational motion of the target at the same time. The time-delay in the photodetachment process will be considered and a scheme to observe the time-delay in photodetachment experiments will be developed.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.