optimizing the searches for interstellar heterocycles

TL;DR

This study uses quantum chemical simulations to optimize the search for interstellar heterocycles, revealing that most are strongly bonded to dust grains except furan, and highlighting the potential detectability of their deuterated analogues in dense molecular clouds.

Contribution

It introduces a two-way quantum chemical approach to assess the detectability of interstellar heterocycles and their deuterated analogues, improving search strategies.

Findings

Furan remains a promising candidate for detection.

Most heterocycles are strongly bonded to dust grains, reducing their abundance.

Deuterated analogues are likely detectable in dense molecular clouds.

Abstract

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.