Electron-stimulated desorption of O- from O2 adsorbed on CD3CN:: Substrate-mediated low-energy reaction pathways

Low-energy (0-15 eV) electron-stimulated desorption of O- from multilayer O-2 proceeds via different O-2(-)* resonances at an onset energy near 6 eV. Ln contrast, O-2 deposited on an acetonitrile (CD3CN) substrate shows a significant contribution towards lower energy with an onset near 2.6 eV, The absolute intensity of this low-energy signal has a maximum at O-2 coverages below 1 monolayer, suggesting a substrate-mediated reaction. It is proposed that the ((2)Pi(CN)) resonance of acetonitrile acts as a low-energy electron acceptor. The energy required for low-energy desorption of O- is then provided by a reaction of the excited anionic complex (CD3CN . O-2)(-)* yielding O- and a thermodynamically favourable neutral species like methylisocyanate (CD3NCO). (C) 1999 Elsevier Science B.V. All rights reserved.