Understanding the impact of diffusion of CO in the astrochemical models
  The mobility of lighter species on the surface of interstellar dust grains
plays a crucial role in forming simple through complex molecules. Carbon
monoxide is one of the most abundant molecules, its surface diffusion on the
grain surface is essential to forming many molecules. Recent laboratory
experiments found a diverse range of diffusion barriers for CO on the grain
surface, their use can significantly impact the abundance of several molecules.
The impact of different diffusion barriers of CO, in the astrochemical models,
is studied to understand its effect on the abundance of solid CO and the
species for which it is a reactant partner. A gas-grain network is used for
three different physical conditions; cold-core and warm-up models with slow and
fast heating rates. Two different ratios (0.3 and 0.5) between diffusion and
desorption barrier are utilized for all the species. For each physical
condition and ratio, six different models are run by varying diffusion barriers
of CO. Solid CO abundance for the models with the lowest diffusion barrier
yields less than 0.1% of water ice for cold clouds and a maximum of 0.4% for
slow and fast warm-up models. Also, solid CO$_2$ in dense clouds is
significantly overproduced (140 % of water). The abundance of H$_2$CO and
CH$_3$OH showed an opposite trend, and HCOOH, CH$_3$CHO, NH$_2$CO, and
CH$_3$COCH$_3$ are produced in lower quantities for models with low diffusion
barriers for CO. Considerable variation in abundance is observed between models
with the high and low diffusion barrier. Models with higher diffusion barriers
provide a relatively better agreement with the observed abundances when
compared with the models having lower diffusion barriers.
