Oxygen as an Electron Scavenger: Its Role in Electron-Induced Activation of Coadsorbed Methane Embedded in Amorphous Solid Water

Low-energy electrons are known to play a fundamental role in activating small molecules in interstellar chemistry. Here we illustrate the electron-induced activation of the inert molecule methane while sandwiched between two 50 monolayers thick layers of amorphous solid water (ASW) on ruthenium substrate at 25 K by employing externally supplied low-energy electrons (5 eV) under ultrahigh vacuum conditions. We demonstrate how electron transmission through ASW layers under cryogenic conditions is strongly affected in the presence of cosandwiched oxygen molecules. We conclude that the resonant nature and direct electron attachment process leads to a higher degree of conversion in the presence of embedded oxygen molecules along with methane. Cross sections ranging from 1 × 10^–18 to 1 × 10^–19 cm²/electrons were obtained from the post-irradiation temperature-programmed desorption spectra.