  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.
