New Method for Simulating Photoprocesses in Astrochemical Models

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Ella Mullikin, Hannah Anderson, Natalie O'Hern, Megan Farrah, Christopher R. Arumainayagam, Ewine F. van Dishoeck, Perry A. Gerakines, Liton Majumdar, Paola Caselli, Christopher N. Shingledecker

We propose a new model for treating solid-phase photoprocesses in interstellar ice analogues. 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 non-thermal, non-diffusive 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 O2. 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 ISM regions. Our results indicate that inclusion of non-thermal reactions and suprathermal species allows for reproduction of low-temperature solid-phase photoprocessing that simulate interstellar ices within cold (∼ 10 K) dense cores such as TMC-1.

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