Dissociative Attachment of Low Energy Electrons: Vibrational Dependence of Negative Ion Formation in Na2 (ν) +e Collisions

Abstract

An essential element of current interest in the characterization of molecular scattering dynamics is the inclusion of internal nuclear motion. Vibrational excitation may play a crucial role in combustion, atmospheric, and plasmas processes. Excited nuclear motion increases the likelihood of deviation from Born-Oppenheimer behavior. Accurate treatment of such phenomena is still a major theoretical challenge.1 We study the influence of vibrational motion on the process of dissociative attachment (DA) of electrons to diatomic molecules. The DA cross section is remarkably sensitive to vibrational excitation; small changes in vibrational excitation can lead to orders of magnitude change in the DA cross section.2-7 Aside from its fundamental importance, research concerning the vibrational dependence of DA has been motivated by the realization that neutral beam heating of controlled fusion plasma may benefit from elevated negative ion production rates associated with DA from vibrationally excited molecules, in particular, from H2.8 More recently, interest has also arisen in the field of micro-electronic device design, where DA can be an important mechanism for controlling electron densities in plasma. The ability to predict the ultimate influence of internal molecular excitation on electron densities may become an important tool in the tailoring of plasmas to the requirements of material processing applications.9 Furthermore, electron induced chemistry on surfaces also involves transient formation of negative ions and the coupling of electronic and nuclear motion.10