Gas-phase spectra of MgO molecules: a possible connection from gas-phase molecules to planet formation

Abstract

A more fine-tuned method for probing planet-forming regions, such as protoplanetary discs, could be rovibrational molecular spectroscopy observation of particular premineral molecules instead of more common but ultimately less related volatile organic compounds. Planets are created when grains aggregate, but how molecules form grains is an ongoing topic of discussion in astrophysics and planetary science. Using the spectroscopic data of molecules specifically involved in mineral formation could help to map regions where planet formation is believed to be occurring in order to examine the interplay between gas and dust. Four atoms are frequently associated with planetary formation: Fe, Si, Mg, and O. Magnesium, in particular, has been shown to be in higher relative abundance in planet-hosting stars. Magnesium oxide crystals comprise the mineral periclase making it the chemically simplest magnesium-bearing mineral and a natural choice for analysis. The monomer, dimer, and trimer forms of (MgO) n with n = 1 − 3 are analyzed in this work using high-level quantum chemical computations known to produce accurate results. Strong vibrational transitions at 12.5 µm, 15.0 µm, and 16.5 µm are indicative of magnesium oxide monomer, dimer, and trimer making these wavelengths of particular interest for the observation of protoplanetary discs and even potentially planet-forming regions around stars. If such transitions are observed in emission from the accretion discs or absorptions from stellar spectra, the beginning stages of mineral and, subsequently, rocky body formation could be indicated.

Rovibrational Considerations for the Monomers and Dimers of Magnesium Hydride and Magnesium Fluoride

“…Similar behavior has been observed for magnesium oxide where the dimer also exhibits lower-frequency fundamentals before going up in the trimer and likely stabilizing in between in the larger structures. 8 In any case, the overall drop in frequency from the monomer to the dimer is expected, and the low-frequency range for such vibrational fundamentals is also expected since only heavy atoms are present. The intensity of this bright peak (359 km/ mol) also nearly doubles in comparison to the monomer, giving further indication of movement toward the bulk, where it is largely opaque in these frequency regimes.…”

“…17−24 Application to Mgbearing molecules has shown promise, 25 especially for magnesium oxide monomer, dimer, and trimer. 8 In order to further explore the spectra of small, magnesium species for applications to both materials science and planet formation, this work will utilize these trusted techniques for the provision of rovibrational data for monomers and dimers of magnesium hydride and magnesium fluoride.…”

Anharmonic Frequencies of (MO)2 and Related Hydrides for M = Mg, Al, Si, P, S, Ca, and Ti and Heuristics for Predicting Anharmonic Corrections of Inorganic Oxides

“… a Previous results from ref . b Denotes imaginary frequency. c Actually C 2 v symmetry. d Double-harmonic intensities at the MP2/6-31+G*/B3LYP/aug-cc-pVTZ levels of theory with the exception of Ca, which used cc-pVTZ for the B3LYP computations. …”

“…In particular, the dimeric forms of the aforementioned monomers would likely occur wherever the monomers do, based on the strong dimerization energy of (MgO) 2 . 26 However, they are more difficult to examine experimentally; their lack of a permanent dipole moment makes them invisible to rotational spectroscopy. Previous computational studies 27,28 show that the lowest-energy isomer of both (AlO) 2 and (SiO) 2 is the cyclic D 2h form, giving a basis for treating the other systems in the same way.…”

“…However, its high computational cost and use of symmetry-internal coordinates that can be difficult to determine for cyclic molecules limit the size and shape of the systems that can be analyzed. previous computational work 26 has elucidated the spectroscopic constants of the cyclic MgO dimer at this state-of-theart level, providing a baseline comparison for the present work.…”