Ground and excited state properties of ThBe and AcBe.

In this work, the ground and excited states of ThBe and AcBe were investigated by performing high-level multireference and single-reference coupled-cluster quantum chemical calculations with large correlation consistent basis sets. Full potential energy curves (PECs), chemical bonding patterns, energetics, spectroscopic parameters (Te, re, ωe, and ωexe), and spin-orbit effects of 13 and 8 electronic states of ThBe and AcBe, respectively, are reported. The ground electronic states of ThBe and AcBe are single-reference 13Σ- (1σ22σ21π2) and 12Π (1σ22σ21π1), respectively, and originate from their corresponding ground state fragments. The chemical bonding of ThBe (13Σ-) and AcBe (12Π) are π-dative in character and are formed by d-electron transfers from Th/Ac to the empty 2px and 2py of the Be atom. The electron populations of the f-orbitals of both ThBe (13Σ-) and AcBe (12Π) are minor which exhibit their "transition-metal-like" nature. The estimated bond energies of the spin-orbit ground states of ThBe (13Σ-0+) and AcBe (12Π1/2) are 12.79 and 11.02 kcal mol-1, respectively. Finally, the bond energy of ThBe was used to estimate its heat of formation ΔH0f(298 K) of 869.61 ± 6 kJ mol-1.