Formation mechanism of complex organic molecules in the interstellar medium

The abundance of atomic hydrogen (H) in the interstellar medium (ISM) makes it a key player in its thermal balance. The formation of molecular hydrogen (H2) in the ISM has long been a topic of interest, as gas-phase models alone cannot account for its large abundance. It is widely believed that carbonaceous dust grains catalyze the formation of H2 through surface-catalyzed reactions. The adsorption of hydrogen on a grain surface is a crucial step in this process, and therefore, plays an important role in interstellar chemistry. While carbon, oxygen, and nitrogen are also major elements in the ISM, their adsorption on carbonaceous materials and suitable models for their reaction remains uncertain. These elements can also react to form H2O and NH3, which have been observed in the ISM. The presence of isomers in different regions of the ISM has also been reported, but the reaction mechanism for their formation is still under investigation. To study the adsorption and reaction of these atomic species on carbonaceous dust grains, density functional theory (DFT) has been used.