Electron-stimulated desorption of $D2O$ coadsorbed with $CO2$ ice at VUV and EUV energies

Electron-induced processes in water ice and $CO2$ ice are important in planetary science. We have measured desorption yields of positive ion products $(C+,$ $O+,$ $D+,$ $D3O+,$ $CO+,$ $O2+)$ produced as a result of exposing pure $CO2$ and $D2O$ adsorbed on $CO2$ ices to 10–100 eV (i.e., the vacuum-ultraviolet–extreme-ultraviolet energy region) electron beams. Measurements on pure $CO2$ ice irradiated with 40-eV electrons suggest that pores in the $CO2$ ice are responsible for trapping molecular precursors for bimolecular reactions that are responsible for $O2+$ production. Investigations of pure $CO2$ ice irradiated with a 100-eV electron beam reveals production of $O2+$ by a second channel attributed to post-ion molecule collisions that are strongly influenced by low-energy electrons trapped in the ice. The most significant finding is that the $D+$ and $D3O+$ yields as a function of both dose and time indicate that the $D2O$ adsorbed on $CO2$ at 30 K diffuses into the $CO2$ ice or desorbs into vacuum very rapidly. Both processes are a result of electron irradiation.