Fundamental Processes in Formation, Dynamics, and Destruction of Molecular Ions in Cold Plasma and Ion Traps

分子等离子体是物质的气态，当相当一部分组成分子被电离时，自由电子和分子离子(缺少电子的分子)移动并相互碰撞。这种相互碰撞的电子和分子离子引发了一系列化学反应，这些过程决定了部分电离气体的各种性质。由于其丰富的化学性质，这类体系在技术上有许多应用。这包括半导体工业，在那里它们被用来制造集成电路。它们也出现在热核聚变努力、医学物理(等离子体治疗)、高功率化学激光和去污染技术中。星际介质和高层大气中存在的分子电离气体的观测使研究人员能够使用地面和空间望远镜研究其性质。为了在应用中有效地使用电离气体，了解和预测不同条件(温度、密度、其他分子的存在等)下电离气体的行为是很重要的。高化学反应性使这一点变得困难。由于这种行为是由电子-离子碰撞等微观过程控制的，因此需要一种量子力学方法来确定性质和预测宏观性质。这就是这项努力的目标。在这个项目中，研究人员专注于两种类型的过程：分子离子在与电子碰撞中的破坏和电子由于辐射而从带负电荷的分子离子中分离。尽管在低温等离子体中电子与中性分子和正分子离子碰撞的基本机制的理论描述取得了重大进展，但仍有一些关键的机制需要发展新的理论方法。理论发展的需要不仅是因为缺乏基本的理解，而且是因为对等离子体工程、等离子体净化技术和空间科学技术的应用非常实际的兴趣。其中一个在应用中非常重要的问题是正分子离子与电子解离复合(DR)碰撞后多原子分子解离时的分支比(BR)：DR中的分支比与产物的电子、振动和旋转态有关，但AMO理论的现状并不能令人满意地描述这个问题。与更冷的系统有关的另一个问题是负分子离子是如何形成和摧毁的。目前还没有令人满意的理论方法来描述光脱离(PD)过程，特别是对于接近脱离阈值的光子能量，旋转通道耦合的情况下，可以解释母体阴离子及其产生的中性分子的振动结构。这项研究计划将集中于两个目标：1.发展一套简单的理论方法来确定小多原子离子在DR中的分支比。BR的理论描述是困难的，因为这个过程涉及入射电子的运动和靶的转动动力学之间的非Born-Oppenheimer耦合。发展了描述多原子阴离子局部放电过程的理论方法，并研究了弱束缚电子态在局部放电和反向过程中的作用--辐射电子附着。在这个项目中，研究人员将开发一种理论方法来描述具有分辨振动结构的分子阴离子中的PD过程，并考虑到正确的近阈值行为和最终状态下的多通道相互作用。该方法将应用于几个在天体物理学中很重要的阴离子，并正在进行实验研究。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Molecular plasma is the gaseous state of matter which occurs when a significant fraction of the constituent molecules are ionized, such that free electrons and molecular ions (molecules with missing electrons) move and collide with each other. Such colliding electrons and molecular ions initiate a network of chemical reactions, and these processes determine various properties of the partially ionized gas. Due to the richness of its chemical properties, such systems have many technological applications. These include the semiconductor industry, where they are used to fabricate integrated circuits. They also occur in thermonuclear fusion efforts, in medical physics (plasma healing), in high-power chemical lasers, and in depollution technologies. The observation of the molecular ionized gas present in the interstellar medium and the upper atmosphere allows researches to study its properties using ground- and space-based telescopes. For its efficient use in applications, it is important to understand and predict the behavior of the ionized gas under different conditions (temperature, density, presence of other molecules, etc.). High chemical reactivity makes this difficult. Because the behavior is governed by microscopic processes such as electron-ion collisions, a quantum mechanical approach is necessary to determine properties and to predict macroscopic properties. That is the goal of this effort. In this project, researchers focus on two types of processes: destruction of molecular ions in collisions with electrons and the detachment of an electron from negatively-charged molecular ions due to radiation. There processes are important for cold molecular plasmas, at room temperature and below.Despite the significant progress in theoretical description of fundamental mechanisms in collisions of electrons with neutral molecules and positive molecular ions in low temperature plasma, there remain a few key mechanisms that require the development of new theoretical methods. The need of the theoretical development is dictated not only by a lack of fundamental understanding, but by very practical interests in applications to plasma engineering, plasma-depolution technologies, and space sciences technologies. One such problem that is extremely important in applications, but not satisfactorily described by the present state of AMO theory, is the branching ratios (BR) in dissociation of polyatomic molecules after a collision of the positive molecular ion with an electron - dissociative recombination (DR): branching ratios in DR with respect to electronic, vibrational, and rotational states of the products. Another problem related to even colder systems is how negative molecular ions are formed and destroyed. There is no satisfactory theoretical approach that can describe the photodetachment (PD) process accounting for the rovibrational structure of the parent anion and the resulting neutral molecule, especially, for photon energies near detachment thresholds, where rotational channels are coupled. This research program will focus on two objectives: 1. The development of a set of simple theoretical approaches to determine branching ratios in DR of small polyatomic ions. A theoretical description of the BR is difficult because the process involves non-Born-Oppenheimer coupling between motion of the incident electron and rovibrational dynamics of the target.2. The development of a theoretical method for the description of the PD process in polyatomic anions and a study of the role of the weakly-bound electronic state in the PD and the inverse process - radiative electronic attachment. In this project the investigators will develop a theoretical method describing the PD process in molecular anions with resolved rovibrational structure and accounting for the correct near-threshold behavior and the multi-channel interaction in the final state. The method will be applied to several anions that are important in astrophysics and being studied experimentally.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.