A New Method for Simulating Photoprocesses in Astrochemical Models

Abstract

We propose a new model for treating solid-phase photoprocesses in interstellar ice analogs. In this approach, photoionization and photoexcitation are included in more detail, and the production of electronically excited (suprathermal) species is explicitly considered. In addition, we have included nonthermal, nondiffusive chemistry to account for the low-temperature characteristic of cold cores. As an initial test of our method, we have simulated two previous experimental studies involving the UV irradiation of pure solid O 2 . In contrast to previous solid-state astrochemical model calculations, which have used gas-phase photoabsorption cross-sections, we have employed solid-state cross-sections in our calculations. This method allows the model to be tested using well-constrained experiments rather than poorly constrained gas-phase abundances in interstellar medium regions. Our results indicate that inclusion of nonthermal reactions and suprathermal species allows for reproduction of low-temperature solid-phase photoprocessing that simulates interstellar ices within cold (∼10 K) dense cores such as TMC-1.