The predicted infrared spectrum of the hyperberyllium molecule BeOBe in its X∼1Σg+ and a˜3Σu+ electronic states

Hypermetallation is a concept that applies to molecules having metal stoichiometries that exceed normal valence, and BeOBe is just one example of such a molecule. Previous ab initio calculations and spectroscopic studies have shown that BeOBe has a linear 1Σg+ ground electronic state and a very low lying 3Σu+ first excited electronic state. As the gas phase infrared spectrum of this molecule is unknown, we simulate such absorption spectra for both of these electronic states. To this end, we calculate the three-dimensional potential energy surfaces and the electric dipole moment surfaces of each of the two states using a multireference configuration interaction (MRCISD) approach based on full-valence complete active space self-consistent field (FV-CASSCF) wavefunctions. This is followed by variational MORBID calculations, using our potential energy and dipole moment surfaces, in order to determine rovibrational term values and to simulate the infrared absorption spectrum of both the singlet and triplet states. We also calculate the dipole polarizability for both states at their equilibrium geometry, as this is of interest for probing the molecule in future beam deflection experiments.