Ab initio electronic structure analysis of ground and excited states of HfN^0,

High-level ab initio electronic structure analysis of third-row transition metal (TM)-based diatomic species is challenging and has been perpetually lagging. In this work, fourteen and eighteen electronic states of HfN and HfN⁺ respectively are studied, employing multireference configuration interaction (MRCI) and coupled cluster singles doubles and perturbative triples [CCSD(T)] theories under larger correlation-consistent basis sets. Their potential energy curves (PECs), energetics, and spectroscopic parameters are reported. Core electron correlation effects on their properties are also investigated. Chemical bonding patterns of several low-lying electronic states are introduced based on the equilibrium electron configurations. The ground state of HfN (X²Σ⁺) has the 1σ²2σ²3σ¹1π⁴ electronic configuration, and the ionization of the 3σ¹ electron produces the ground state of HfN⁺ (X¹Σ⁺). Ground states of both HfN and HfN⁺ are triple bonded in nature and bear 124.86 and 109.10 kcal mol^-1 binding energies with respect to their ground state fragments. The findings of this work agree well with the limited experimental literature available and provide useful reference values for future experimental analysis of HfN and HfN⁺.