“…Such systems play a vital role in areas from industrial [1] and biological [2] catalysts, to astrophysics [3]. Nickel monohalides (NiX; X = F, Cl, Br or I), have received much attention in recent years, and the electronic structure of NiF [4,5] and NiCl [6][7][8][9][10][11] is now relatively well understood, while the ground state of NiBr has also been identified [12,13]. The close proximity of the low-lying electronic states in these species results in many perturbations, and the application of high resolution spectroscopic techniques, together with thorough theoretical investigation, has resulted in an improved understanding of the electronic structure of these species.…”