The vacuum ultraviolet pulsed field ionization-photoelectron and photoionization efficiency spectra of NCCN have been measured in the energy region of 13.25-17.75 eV. The analyses of these spectra have provided accurate ionization energy (IE) values of 13.371 +/- 0.001, 14.529 +/- 0.001, 14.770 +/- 0.001, and 15.516 +/- 0.001 eV for the formation of NCCN+ in the X(2)Pi(g), A(2)Sigma(g)(+), B(2)Sigma(u)(+), and C(2)Pi(u) states, respectively. The ionization energy [NCCN+(B(2)Sigma(u)(+))] value determined here indicates that the origin of the NCCN+(B(2)Sigma(u)(+)) state lies lower in energy by 25 meV than previously reported. A set of spectroscopic parameters for NCCN+(X(2)Pi(g)) has been calculated using high level ab initio calculations. The experimental spectra are found to consist of ionizing transitions populating the vibronic levels of NCCN+, which consist of pure vibronic progressions, combination modes involving the symmetric CN stretch, the CC stretch, and even quanta of the antisymmetric CN stretch, and bending vibrations. These bands are identified with the guidance of the present ab initio calculations. (c) 2005 American Institute of Physics.