Resonant two-photon ionization spectroscopy of NiC

A spectroscopic investigation of jet-cooled diatomic NiC has revealed a complex pattern of vibronic levels in the wave number range from 21 700 to 27 000 cm−1. Of the more than 50 vibronic bands observed, 31 have been rotationally resolved and analyzed. All are Ω′=0+←Ω″=0+ transitions, consistent with the calculated Σ+1 ground state of this molecule. Through the observation of vibrational hot bands in the spectra, these measurements have established that ωe″=875.155 cm−1, ωexe=5.38 cm−1, Be=0.640 38(14) cm−1, αe=0.004 44(36) cm−1, and re=1.6273(2) Å for Ni58C12. Several possible electronic band systems are observed, but the identification of these is hampered by extensive perturbations among the excited states. The observation of long-lived vibronic states as far to the blue as 26 951 cm−1 indicates that D0(NiC)⩾3.34 eV, and the ionization energy of NiC has been determined to fall in the range IE(NiC)=8.73±0.39 eV. A discussion of these results, in the context of work on other 3d transition metal carbides is also presented.