Formation and Destruction of Molecular Ions in Collisions with Electrons in the Interstellar Medium

分子和原子的“阴离子”是电子碰撞并附着在分子或原子上时形成的微观粒子。阴离子在各种环境中发挥着重要作用，在技术和基础研究中有着广泛的应用。在这些应用中，不仅有烟雾探测器等普通产品，还有更复杂的设备，包括聚变反应堆（将大量光原子转化为电能的设备，可能是21世纪下半叶清洁能源的主要来源）。阴离子在半导体技术中发挥着重要作用，由于在星际空间和大型行星的大气中发现了阴离子，因此对航天工业具有重要意义。尽管它的重要性和许多用途，阴离子的形成是知之甚少。这是因为涉及电子与分子碰撞的过程很难从理论上描述。在某些情况下，可以通过做适当的实验来克服缺乏理论认识。然而，实验是昂贵的，特别是在没有理论指导的情况下。一个例子是在等离子体中使用阴离子，由于聚变发生所需的极端温度，实验成本很高。本研究的目的是了解和模拟与星际介质、行星大气和技术发展有关的分子阴离子形成过程。拟议的研究计划是一个跨学科的努力，涉及天体物理学、行星科学和等离子体物理学。该项目将回答观察到的分子阴离子是如何在冷等离子体中形成的（比如在星际介质或行星的高层大气中），以及它们形成和破坏的速度。该项目将开发理论方法，可用于科学界研究其他类似过程。这个项目解决了一些与分子等离子体基本过程有关的原子和分子物理问题。分子等离子体的演化和衰变是由电子和分子（或分子离子）之间的碰撞控制的。了解这些基本过程对于研究实验室等离子体、行星大气和星际介质（ISM）非常重要。它还允许人们开发用于建模、监测和控制等离子体的工具，这对于半导体蚀刻或托卡马克等离子体壁保护等技术应用至关重要。本项目主要致力于研究辐射电子附着（REA）和解离电子附着（DEA）形成负分子离子。这项研究的动机是最近在ISM中检测到负离子CnH- (n=4,6,8)和CnN- (n=1,3,5)。这些离子（CN-除外）可能是由REA在ISM中形成的。近年来，本课题组提出了一种计算REA速率系数的全量子方法，并应用于研究CN-中的REA。发现CN-的REA生成速率系数很低。对于较大的分子离子，全量子方法可能会给出较小的速率系数，这意味着观察到的离子的ISM丰度不能用REA来解释。该项目的一个目标是将开发的全量子方法应用于其他观察到的分子离子：负离子形成的REA机制将使用第一性原理进行研究。这项研究的结果很可能会导致对阴离子形成机制的修订。随后，所开发的方法将应用于研究星际介质、行星大气和实验室等离子体中阴离子和阳离子化学的几个问题。特别是，在ISM中阴离子形成的解离机制或辐射机制是否更有效的问题将被解决。该项目将有助于发展与等离子体有关的数据库，特别是那些用于模拟磁聚变装置、行星大气、航天器再入大气层和星际介质的数据库。

Molecular and atomic "anions" are microscopic particles formed when an electron collides and attaches to a molecule or an atom. Anions play an important role in various environments and have many applications in technology and fundamental research. Among these applications are not only common products such as smoke detectors, but also much more sophisticated devices, including fusion reactors (devices that transform the mass of light atoms into into electricity and which may be a major source of clean energy for the second half of the 21st century). Anions play an important role in semiconductor technology and have important implications for the space industry since they have been found in interstellar space and the atmospheres of large planets. Despite its importance and many uses, the formation of anions is poorly understood. This is because the process involving collisions of electrons with molecules is difficult to describe theoretically. In some situations, it is possible to overcome the lack of theoretical understanding by doing the appropriate experiments. However, experiments are expensive, especially if no theoretical guidance is available. An example is the use of anions in plasmas, where experiments are expensive because of the extreme temperatures needed for fusion to occur. The aim of this research is to understand and model the process of molecular anion formation in relation to the interstellar medium, planetary atmospheres, and technology development. The proposed research program is a cross disciplinary effort involving astrophysics, planetary science, and plasma physics. The project will answer the question of how observed molecular anions are formed in cold plasmas (such as in the interstellar medium or upper atmosphere of planets) and also how fast they are formed and destroyed. The project will develop theoretical methods that could be used by the scientific community to study other similar processes. This project addresses a number of atomic and molecular physics problems related to elementary processes in molecular plasmas. Molecular plasma evolution and decay are governed by collisions between electrons and molecules (or molecular ions). Understanding such elementary processes is important in studies of laboratory plasmas, planetary atmospheres, and the interstellar medium (ISM). It also allows one to develop tools for modeling, monitoring, and controlling plasmas, which is crucial for technological applications such as semiconductor etching or tokamak plasma wall protection in the divertor region. The project is mainly devoted to the study of the formation of negative molecular ions by radiative electron attachment (REA) and dissociative electron attachment (DEA). The study is motivated by a recent detection of negative ions CnH- (n=4,6,8) and CnN- (n=1,3,5) in the ISM. It was suggested that these ions (except, maybe, CN-) are formed in the ISM by REA. Recently, a fully-quantum method to calculate the REA rate coefficients was developed in the group and applied to study REA in CN-. A very low rate coefficient for REA formation of CN- was found. For larger molecular ions, the fully-quantum method will likely give rate coefficients that are also small, which would mean that the observed ISM abundance of the ions cannot be explained by REA. One goal of the project is to adapt the developed fully-quantum method to other observed molecular ions: The REA mechanism of negative ion formation will be studied using first principles. It is likely that results of this study will lead to a revision of the accepted mechanisms of anion formation in the ISM. Later, the developed methods will be applied to study several problems in the chemistry of anions and cations in the interstellar medium, planetary atmospheres, and laboratory plasmas. In particular, the question of whether the dissociative or radiative mechanism of anion formation in the ISM is more efficient will be addressed. The project will contribute to the development of plasma-related databases, in particular, those used for modeling magnetic fusion devices, planetary atmospheres, spacecraft re-entry, and interstellar medium.