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

分子和原子“阴离子”是当电子碰撞并附着到分子或原子上时形成的微观粒子。 阴离子在各种环境中起着重要的作用，在技术和基础研究中有许多应用。在这些应用中，不仅有烟雾探测器等常见产品，还有更复杂的设备，包括聚变反应堆（将轻原子质量转化为电能的设备，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，并对航天工业具有重要意义，因为它们在星际空间和大型行星的大气中被发现。尽管它的重要性和许多用途，形成的阴离子是知之甚少。这是因为电子与分子碰撞的过程很难在理论上描述。在某些情况下，可以通过做适当的实验来克服理论理解的缺乏。然而，实验是昂贵的，特别是如果没有理论指导。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，实验是昂贵的。这项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如何在冷等离子体中形成的问题（例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有多快。该项目将开发可供科学界用于研究其他类似过程的理论方法。本计画主要研究与分子电浆基本过程相关的原子与分子物理问题。分子等离子体的演化和衰变由电子和分子（或分子离子）之间的碰撞控制。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。它还允许开发用于建模，监测和控制等离子体的工具，这对于偏滤器区域中的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。该项目主要致力于研究通过辐射电子附着（REA）和解离电子附着（DEA）形成负分子离子。本研究的动机是最近在ISM中检测到的负离子CnH-（n= 4，6，8）和CnN-（n= 1，3，5）。这些离子（可能除了CN-）都是在ISM中通过REA形成的。最近，该小组发展了一种计算REA速率系数的全量子方法，并应用于CN-中的REA研究。对于较大的分子离子，全量子方法可能给出的速率系数也很小，这意味着所观察到的离子的ISM丰度不能用REA来解释。该项目的一个目标是使开发的全量子方法适用于其他观察到的分子离子：将使用第一性原理研究负离子形成的REA机制。这是可能的，这项研究的结果将导致在ISM中的阴离子形成的公认的机制的修订。后来，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，是否在ISM中的阴离子形成的解离或辐射机制是更有效的问题将得到解决。该项目将有助于开发与等离子体有关的数据库，特别是用于模拟磁聚变装置、行星大气层、航天器重返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.