A New Method for Simulating Photoprocesses in Astrochemical Models

TL;DR

This paper introduces a detailed new astrochemical model that explicitly includes solid-phase photoprocesses, suprathermal species, and non-thermal chemistry, improving the simulation of interstellar ice photoprocessing at very low temperatures.

Contribution

The novel model incorporates solid-state cross-sections, suprathermal species, and non-thermal reactions, enhancing the accuracy of astrochemical simulations of cold interstellar ices.

Findings

Model reproduces low-temperature photoprocessing in interstellar ices.

Solid-state cross-sections improve agreement with experiments.

Non-thermal reactions are crucial for simulating cold core chemistry.

Abstract

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 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 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 ($\sim$ 10 K) dense cores such as TMC-1.