Electronic structure and chemical bonding of the MoBe molecule

Molybdenum beryllium materials are being researched and applied in cutting-edge technologies. It has been found that beryllium, even though it has a full 2s subshell, can form a variety of bonds with specific atoms. Here, the simple building block, the MoBe molecule, is investigated to shed light in their bonding. Specifically, forty-three low-lying states of MoBe have been investigated via complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCISD(+Q)) using the aug-cc-pV5Z(-PP) basis set. Dissociation energies (D_e), dipole moments, and various spectroscopic constants are calculated, while potential energy curves are plotted. A variety of bonding is formed in MoBe, i.e., half bonds up to the formation of triple bonds, while in most cases, Be atoms are excited at the Be(³P) state. The ground state, X⁷Σ⁺, is well separated from the excited ones, i.e., the first excited state, a⁵Σ⁺, is lying 15.0 kcal mol^-1 above. The adiabatic D_e of calculated states range from 2.5 (⁹Σ⁺(1), van der Waals interaction) to 57.7 kcal mol^-1 (b⁵Π). The b⁵Π, ³Δ(1), and ³Π(1) have triple bonds, while their diabatic D_e values are 86.7, 92.0 and 88.0 kcal mol^-1. The MRCISD+Q bond distances range from 2.047 (³Δ(1)) to 2.787 Å (⁹Σ⁺(1)), while dipole moments range from 1.51 to 3.28 D. Overall, the present work highlights the exceptional ability of beryllium atoms to participate in a variety of bonding schemes, and it could provide the opening gate for further investigation of this species or associated materials and complexes.