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 O2 proceeds via different O2−* resonances at an onset energy near 6 eV. In contrast, O2 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 O2 coverages below 1 monolayer, suggesting a substrate-mediated reaction. It is proposed that the (2ΠCN) 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·O2)−* yielding O− and a thermodynamically favourable neutral species like methylisocyanate (CD3NCO).