Binding Energy and Isomerism: Two Important Aspects of Astrochemistry

Abstract

Hydrogen is widespread in the universe and H₂, the precursor to more complex molecules, is mainly formed on the interstellar dust grain surface and binding energy dictates the surface chemistry. We review the adsorption energy of H and H₂ to find out the accurate formation efficiency of hydrogen molecules in the interstellar medium (ISM). Various types of substrate (carbonaceous, olivine, and water ice) were used to mimic interstellar dust grain. Interestingly we found that our calculated binding energy of H is always lower than that of H₂ for all types of adsorbent considered, whereas, some experiments found just the opposite trend. Though the ISM is far away from thermodynamic equilibrium, in some cases, isomerism of any specific group of molecules can be used as a way to determine the potential future observable candidates in interstellar space. Understanding the origin of life is a traditional mystery and it is curious to know how life emerged in the universe. We considered a set of molecules from various isomeric groups containing some probable precursors of the pre-biotic species to review their presence within ISM. For the selection of potentially observable molecules in between an isomeric group, we used some key tools such as enthalpies of formation, optimized energies, expected intensity ratio, and chemical abundances. According to our calculations, we proposed trans-ethylamine and (1Z)-1-propanimine as the most probable candidates from two different isomeric groups for future astronomical detection.