Usman Lawal

By Etim Emmanuel, Lawal Usman, Khanal Govinda and Mbakara Idaresit

Out of the 19 known S-containing interstellar molecules, 16 have the corresponding O-compound analogues marks out of the interstellar chemistry of sulfur and oxygen as a unique one among other observed interstellar periodic trends. However, the rule that the ratio of an interstellar sulfur molecule to its oxygen analogue is close to the cosmic S/O ratio is far from reality in many cases even when both species are observed from the same source. In this chapter, the effect of interstellar hydrogen bonding on the variation of the S/O abundance ratio with respect to the cosmic S/O ratio is investigated using high-level quantum chemical simulations. The detectability of the yet to be observed analogues of both S and O molecules is also examined. From the results, the deviation from the cosmic S/O ratio is largely due to hydrogen bonding on the surface of the dust grains. As the ratio of the binding energy of S- and O-species (binding energy of S/O) with water approaches unity, the S/O abundance ratio approaches cosmic S/O ratio. The more this ratio deviates from unity, the more the S/O abundance deviates from the cosmic S/O ratio. Regarding the detectability of the unknown analogues, it suffices to say that every known O-species is an indication of the presence and detectability of the S-analogue, while for every known S-species, the O-analogue is not only present in detectable abundance, it can be said to have even been overdue for astronomical detection.

Part of the book: Basic Concepts Viewed from Frontier in Inorganic Coordination Chemistry