  Complex organic molecules (COMs) have been detected in a variety of
interstellar sources. The abundances of these COMs in warming sources can be
explained by syntheses linked to increasing temperatures and densities,
allowing quasi-thermal chemical reactions to occur rapidly enough to produce
observable amounts of COMs, both in the gas phase, and upon dust grain ice
mantles. The COMs produced on grains then become gaseous as the temperature
increases sufficiently to allow their thermal desorption. The recent
observation of gaseous COMs in cold sources has not been fully explained by
these gas-phase and dust grain production routes. Radiolysis chemistry is a
possible non-thermal method of producing COMs in cold dark clouds. This new
method greatly increases the modeled abundance of selected COMs upon the ice
surface and within the ice mantle due to excitation and ionization events from
cosmic ray bombardment. We examine the effect of radiolysis on three
C$_{2}$H$_{4}$O$_{2}$ isomers -- methyl formate (HCOOCH$_3$), glycolaldehyde
(HCOCH$_2$OH), and acetic acid (CH$_3$COOH) -- and a chemically similar
molecule, dimethyl ether (CH$_3$OCH$_3$), in cold dark clouds. We then compare
our modelled gaseous abundances with observed abundances in TMC-1, L1689B, and
B1-b.
