Ground and excited state properties of ThB^- and ThB: a theoretical study

In the present work, we studied a series of electronic and spin-orbit states of ThB^- and ThB using high-level multireference and coupled-cluster theories. We report the potential energy curves (PECs), equilibrium electron configurations, spectroscopic constants, energetics, and spin-orbit coupling effects of 17 and 19 electronic states of ThB^- and ThB, respectively. The ground state of ThB^- is a single-reference 1³Π with a 1σ²2σ²3σ¹1π³ electron configuration. Detachment of an electron from the doubly occupied 1π orbital of ThB^-(1³Π) produces the single-reference ground electronic state of ThB (1⁴Σ^-). The ground spin-orbit states of ThB^- and of ThB are 1³Π+0 and 1⁴Σ-3/2, respectively. The vertical electron detachment energy (VDE) of ThB^- and the adiabatic electron attachment energy (AEA) of ThB at our largest CBS-C-CCSD(T)+δT(Q)+δSO (complete basis set effect, spin-orbit effect, and triple and perturbative quadruple electron correlation effect added coupled-cluster theory with single, double, and perturbative triple excitations) level are 1.473 eV and 1.459, respectively. The reaction of Th(³F) + B(²P^o) produces the ground state of ThB with a bond energy of 2.843 eV. Finally, we estimated a heat of formation, ΔH0f (298 K), of 891.01 kJ mol^-1 for the ThB molecule. The high-level findings of this work are expected to aid and motivate future experimental spectroscopic investigations of ThB and ThB^- species.