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

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

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.