  Recent detections of aromatic species in dark molecular clouds suggest
formation pathways may be efficient at very low temperatures and pressures, yet
current astrochemical models are unable to account for their derived
abundances, which can often deviate from model predictions by several orders of
magnitude. The propargyl radical, a highly abundant species in the dark
molecular cloud TMC- 1, is an important aromatic precursor in combustion flames
and possibly interstellar environments. We performed astrochemical modeling of
TMC-1 using the three-phase gas-grain code NAUTILUS and an updated chemical
network, focused on refining the chemistry of the propargyl radical and related
species. The abundance of the propargyl radical has been increased by half an
order of magnitude compared to the previous GOTHAM network. This brings it
closer in line with observations, but it remains underestimated by two orders
of magnitude compared to its observed value. Predicted abundances for the
chemically related C4H3N isomers within an order of magnitude of observed
values corroborate the high efficiency of CN addition to closed-shell
hydrocarbons under dark molecular cloud conditions. The results of our modeling
provide insight into the chemical processes of the propargyl radical in dark
molecular clouds and highlight the importance of resonance-stabilized radicals
in PAH formation.
