Studies of Electron Attachment to Stable Molecules and Radicals, Ion-ion Neutralization, and Electron-catalyzed Reactions at Thermal Energies

Presented by Thomas Miller, Boston College and the Air Force Research Laboratory

Electron attachment rate constants and products have been studied over a temperature range from 300 to as high as 1100 K in a flowing-afterglow Langmuir-probe (FALP) apparatus originally constructed at the University of Oklahoma. This work has resulted in new information on even the most-studied molecule of all, SF6, as well as for related molecules such as SF5C6H5, and sulfur oxyhalides, transition-metal fluorides and trifluorophosphines, freons, Cl2, SO3, O3, NF3, PF5, ClONO2, and many organic compounds. Experiments have just been completed on electron attachment to chlorine azide (ClN3), which is a reactant in the AGIL laser (all-gas iodine laser) and is the starting point for generating what is thought to be cyclic-N3. The FALP method has also been used to study negative ion mutual neutralization with Ar+. Our initial publication on ion-ion neutralization noted the presence of "unexpected" negative ions in the mass spectra at high electron densities, such as SF4- from work with SF6 and PSCl- from work with PSCl3. We have now identified the source of these unexpected ions as due to electron attachment to radicals produced in the initial attachment reaction and in ion-ion neutralization, and are able to deduce rate constants for the secondary attachment and for ion-ion neutralization. At high electron densities (>10^10 cm-3) we observe what appears to be electrons acting as a third body in enhancing negative ion neutralization with Ar+. While ternary reactions with neutral third bodies are well known, the electron-catalyzed reaction presents an interesting new theoretical problem.