Electron Attachment to Molecules of Practical Applications

Abstract

Qualitative and quantitative data on electron-molecule collisions are important for a wide variety of applications from planetary atmospheric modelling, astro-chemistry, pollution control, radiation damage, analytical mass spectrometry, fusion plasma devices, dry etching machines for semiconductor fabrication, high current switches and insulators1. One of the very important processes in low energy electron-molecule collisions is the formation of negative ions through dissociative attachment2. In this process an electron of a particular energy interacts with a given molecule to form a negative ion resonance. This resonance subsequently decays through autodetachment in which the electron escapes into the continuum, leaving the molecule in a vibrationally excited state in certain situations. The negative ion resonance may also decay through a dissociation process depending on its potential energy surface. However this dissociation process is dependent on the lifetime of the resonance against autodetachment and is also very sensitive to the internuclear separation. Several experiments involving vibrational excitation have shown that this process is very sensitive to initial vibrational excitation of the neutral molecule2, 3, 4, 5. In addition, as electronic excitation leads to large changes in the polarizability and structure and symmetry of a molecule, one may expect corresponding changes in the resonant attachment and dissociation process.