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

Abstract

Magnesium is an understudied chemical element that is quite useful in materials science and may be an essential astrochemical building block for grain formation in proto-planetary disks. This work provides quantum chemical prediction for the vibrational and rovibrational spectra of the structurally similar magnesium hydride and magnesium fluoride monomers and dimers. Magnesium fluoride is commonly utilized in infrared-observing windows and is a known terrestrial mineral, sellaite. Magnesium hydride is likely to exist in various astrophysical environments. Comparison of the anharmonic quantum chemical spectral data computed in this work to known gas phase values for MgH is excellent with the computed 1584.1 cm antisymmetric Mg-H stretch less than 5 cm below experiment for example. The condensed phase vibrational attributions of the dimer, however, are less comparable with the present results potentially indicating that some of the previous assignments may need to be revisited. The magnesium fluoride monomer and dimer have no previous vibrational experimental results reported, and the work here should be solid predictions as to their spectral features for comparison either to laboratory work or potentially even to interstellar observations.

The performance of explicitly correlated methods for the computation of anharmonic vibrational frequencies

“…Such has been proposed as a means of computing vibrational frequencies and other spectroscopic values, but results have been mixed. However, recent work has shown that CCSD(T)‐F12b with a triple‐zeta basis set may achieve a nice Pauling point for a cancellation of errors generating fundamental vibrational frequencies that are closely coincident with much more costly CcCR QFF VPT2 results . However, the reliability of such an overlap has not been systematically documented.…”

“…However, recent work has shown that CCSD(T)-F12b with a triple-zeta basis set may achieve a nice Pauling point for a cancellation of errors generating fundamental vibrational frequencies that are closely coincident with much more costly CcCR QFF VPT2 results. [29][30][31] However, the reliability of such an overlap has not been systematically documented. This work will do just that comparing CCSD(T)-F12 QFF results (as well as those from MP2-F12) with those from both previous CcCR values and those from experiment where available.…”

Further Astrochemical Insights From Bond Strengths of Small Molecules Containing Atoms From the First Three Rows of the Periodic Table

“…The diatomic species that contain these bonds have an equal number of valence electrons occupying bonding and antibonding orbitals, which yields a bond order of 0, meaning that bond formation is not energetically favorable much like that present in noble gas dimers. Additionally, group 2 elements prefer 180°bond angles implying a strong preference for the valence electrons to be found on opposite sides of the atoms (Bassett and Fortenberry, 2018;Palmer and Fortenberry, 2018;Doerksen and Fortenberry, 2020;Watrous et al, 2021). In returning to the bond lengths, the Be Be, Be Mg, and Mg Mg bonds are close to the sum of their constituent atom's Van der Waals radii rather than their covalent radii.…”

ArCH2+: A Detectable Noble Gas Molecule

“…[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] The geometries are optimized with coupled cluster singles, doubles, and perturbative/parenthetical triples [CCSD(T)] [45] with the augcc-pV5Z basis set. [46][47][48] The reader should note that all computations for the argon atom contain the additional ðX þ dÞ orbitals. This minimum structure is then refined with geometrical considerations for the nuclear response to core electrons in the wavefunction through CCSD(T) geometry optimizations with the Martin-Taylor (MT) correlating basis set [49] .…”

“…The same procedure utilized to produce rotational constants to within 30 MHz and vibrational frequencies to within 5 cm −1 and sometimes even 1 cm −1 will be utilized here . The geometries are optimized with coupled cluster singles, doubles, and perturbative/parenthetical triples [CCSD(T)] with the aug‐cc‐pV5Z basis set .…”