Astrochemistry Does Not (Always) Need Carbon: Insights from Computation

The elemental abundances of rocky bodies are vastly different from the Universe at large. Our Earth is a rocky planet largely composed of oxygen followed by notable amounts of silicon, magnesium, iron, and some aluminum. However, before these atoms can form rocks which form planets, they likely must first form small molecules which can form nanocrystals and then rocks. This class of small, inorganic molecules has largely been unexplored in the chemical literature. These quantum chemical studies have analysed small inorganic oxides and hydrides and have found a notable similarity between bond strengths of inorganic hydrides and elemental abundances. Additionally, hydrogenated monomers of the mineral corundum (ruby and sapphire are part of this geomorphological family) have been shown to form with only submerged barriers from the association of water with alane (AlH₃). This has also been shown for periclase monomers and dimers from water and magnesium hydride (MgH₂). In order to support such reactions, the rovibrational spectral properties of the minima along these pathways are being computed using quartic force fields and state-of-the-art electronic structure methods. Hence, these or related molecules may help to explain portions of unattributed IR spectra as well as provide evidence for the early stages of nanocrystal formation in protoplanetary disks leading to planet formation. Conversely, the presence of these molecules in planetary nebulae, supernova remnants, or other stellar corpses may indicate the previous existence of rocky planets in former planetary systems.