Secondary Ion-Ice Chemistry in UV-Irradiated Oxygen Ice: New Astrochemical Models Including Bulk Ionic Species

Although energetic and nonenergetic processing of interstellar dust grain surfaces and ice is thought to be one of the dominant mechanisms for the extraterrestrial synthesis of prebiotic molecules, the role that "ion-ice" chemistry (bulk ion-neutral and ion-ion reactions within the dust-grain ice mantle) plays is still a largely unexplored topic. In this work, we present the results of our study to investigate the astrochemical importance of ions produced within dust grain ice mantles via irradiation by VUV photons, though the methods are applicable to other kinds of ionizing radiation. To this end, we present new models of the chemical evolution of a pure oxygen ice irradiated by UV photons, using a chemical network that explicitly includes bulk reactions involving secondary ions. A comparison of our calculations with previous data suggests that ion-neutral and ion-ion reactions may play a critical role in understanding the chemistry of interstellar ice.