  The icy mantles of interstellar dust grains are the birthplaces of the
primordial prebiotic molecular inventory that may eventually seed nascent solar
systems and the planets and planetesimals that form therein. Here, we present a
study of two of the most abundant species in these ices after water: carbon
dioxide (CO2) and methanol (CH3OH) using TeraHertz (THz) time-domain
spectroscopy and mid-infrared spectroscopy. We study pure and mixed-ices of
these species, and demonstrate the power of the THz region of the spectrum to
elucidate the long-range structure (i.e. crystalline versus amorphous) of the
ice, the degree of segregation of these species within the ice, and the thermal
history of the species within the ice. Finally, we comment on the utility of
the THz transitions arising from these ices for use in astronomical
observations of interstellar ices.
