Spectroscopy and electronic structure of the hypermetallic oxide, MgOMg

Electronic spectra for the hypermetallic oxide MgOMg have been observed in the 21 100 cm^-1-24 000 cm^-1 spectral range using laser induced fluorescence and two-photon resonantly enhanced ionization techniques. Rotationally resolved data confirmed the prediction of a X̃¹Σ_g ⁺ ground state. The spectrum was highly congested due to the optical activity of a low-frequency bending mode and the presence of three isotopologues with significant natural abundances. Ab initio calculations predict a bent equilibrium structure for the ùB₂ upper state, consistent with the observation of a long progression of the bending vibration mode. However, the vibrational intervals were not reproduced by the theoretical calculations. In part, this discrepancy is attributed to strong vibronic coupling between multiple electronically excited states. Two-photon ionization measurements were used to determine an ionization energy of 6.5800(25) eV.