  It is a fact that interstellar formation processes are thermodynamically
affected. Based on this, the seven heterocycles; imidazole, pyridine,
pyrimidine, pyrrole, quinoline, isoquinoline and furan that have been searched
for from different astronomical sources with only upper limits of their column
density determined without any successful detection remain the best candidates
for astronomical observation with respect to their isomers. These molecules are
believed to be formed on the surface of the interstellar dust grains and as
such, they are susceptible to interstellar hydrogen bonding. In this study, a
two way approach using ab initio quantum chemical simulations is considered in
optimizing the searches for these molecules in interstellar medium. Firstly,
these molecules and their isomers are subjected to the effect of interstellar
hydrogen bonding. Secondly, the deuterated analogues of these heterocycles are
examined for their possible detectability. From the results, all the
heterocycles except furan are found to be strongly bonded to the surfaces of
the interstellar dust grains thereby reducing their abundances, thus
contributing to their unsuccessful detection. Successful detection of furan
remains highly feasible. With respect to their D-analogues, the computed
Boltzmann factor indicates that they are formed under the dense molecular cloud
conditions where major deuterium fractionation dominates implying very high D/H
ratio above the cosmic D/H ratio which suggests the detectability of these
deuterated species.
