The formation of CO2 in quiescent molecular cores has long been of interest to
astrochemists as CO2 is one of the most abundant solid phase molecules present
in the interstellar medium. Previous studies have concentrated, for the most part, on
formation mechanisms involving high energy particle or UV bombardment of ices, to mimic
the influence of cosmic rays on solid phase species in the outer, lower density regions of
molecular clouds. However, condensed phase CO2 is also observed in the inner,
denser regions of clouds, where less UV radiation penetrates. To date, very few studies
have been made of CO2 formation in the absence of energetic particles.
Low-energy routes to the formation of CO2 are crucial to explain the high
abundances of this molecule observed in quiescent regions. We discuss recent experimental
results of a study of the low-energy reaction CO + OH. A simple model, developed to
describe the kinetics of the system, suggests that the various reactions of the OH radical
are key in characterising the production of CO2 and other species. Our results
indicate that some CO2 forms concurrently with H2O in molecular
clouds, in line with both previous observations and theory. The results of this research
are published in Noble et al.