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

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

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.