Theoretical Rotational and Vibrational Spectral Data for the Hypermagnesium Oxide Species Mg2O and Mg2O+

While magnesium is astronomically observed in small molecules, it largely serves as a contributor to silicate grains, though how these grains form is not well-understood. The smallest hypermagnesium oxide compounds (Mg2O/Mg2O+ ) may play a role in silicate formation, but little vibrational reference data exist. As such, anharmonic spectroscopic data are computed for X-1 Sigma Mg-+(g)2 O, a(1)Sigma+uMg2O, and X-2 Sigma+gMg2O using quartic force fields (QFFs). Explicitly-correlated coupled-cluster QFFs for the neutral species perform well, implying that full multireference treatment may not be necessary for such systems if enough electron correlation is included. Equation-of-motion ionization potential (EOMIP) methods for X-2 Sigma Mg-+(g) O-2(+) QFFs circumvent previous symmetry breaking issues even in explicitly-correlated coupled-cluster results, motivating the need for EOMIP treatments at minimum for such systems. All three species are found to have high-intensity vibrational frequencies. Even so, the highly intense frequency ( X-1 Sigma+gMg2O: 894.7 cm(-1)/11.18 mu m; a(1)Sigma+uMg2O: 915.0 cm(-1)/10.91 mu m) for either neutral state may be astronomically obscured by the polycyclic aromatic hydrocarbon 11.2 mu m band. Mg2 O+ may be less susceptible to such obfuscation, and its v(1 ) intensity is computed to be a massive 4793 km mol(-1).