Rovibronically selected and resolved two-color laser photoionization and photoelectron study of nickel carbide cation

We have performed a two-color laser photoionization and photoelectron study of nickel carbide (NiC) and its cation (NiC+). By preparing NiC in a single rovibronic level of an intermediate vibronic state via visible laser excitation prior to ultraviolet laser photoionization, we have measured the photoionization efficiency spectrum of NiC near its ionization threshold, covering the formation of NiC+(X 2Σ+;v+=0-3). We have also obtained well-resolved rotational transitions for the v+=0 and 1 vibrational bands of the NiC+(X 2Σ+) ground state. The assignment of rotational transitions observed between the neutral NiC intermediate state and the NiC+ ion ground state has allowed the direct determination of a highly precise value for the ionization energy of NiC, IE(NiC)=67 525.1±0.5 cm-1 (8.372 05±0.000 06 eV). This experiment also provides reliable values for the vibrational spacing [ΔG(1/2)=859.5±0.5 cm-1], rotational constants (Be+=0.6395±0.0018 cm-1 and αe+=0.0097±0.0009 cm-1), and equilibrium bond distance (re+=1.628 A) for the NiC+(X 2Σ+) ground state. The experimental results presented here are valuable for benchmarking the development of more reliable ab initio quantum computation procedures for energetic and spectroscopic calculations of transition metal-containing molecules.