The electronic spectrum of NiCN in the visible region

The electronic spectrum of NiCN in the 500-630 nm region has been observed by laser-induced fluorescence, following the reaction of laser-ablated nickel atoms with cyanogen under free jet expansion conditions. Seven electronic states hake been identified. Three of these, (X) over tilde (1) (2)Delta(5/2), (X) over tilde (2) (2)Delta(3/2), and (W) over tilde (2)(1)Pi(3/2), are derived from the electron configuration Ni+ (3d(8) 4s) CN, and the other four, (A) over tilde (2) Delta(5/2), (B) over tilde (2)Pi(3/2), (C) over tilde (2)Phi(7/2) and (D) over tilde (2)Phi(5/2), are derived from the configuration Ni+ (3d(8) 4s) CN. Rotational analysis of bands of (NiCN)-N-14 and (NiCN)-N-15 at high resolution has given the bond lengths in the (X) over tilde (2)(1)Delta(5/2) ground state as r(0) (Ni-C) = 1.8292 +/- 0.0028 Angstrom; r(0) (C-N) = 1.1591 +/- 0.0029 Angstrom. The orbital angular momentum splits the bending fundamental of the (X) over tilde (2)(1)Delta(5/2) state into two vibronic components, which lie at 243.640 cm(-1) ((2)Pi(3/2)) and 244.964 cm(-1) ((2)Phi(7/2)). Exceptionally strong Fermi resonance occurs in the ground state between the Ni-C stretching vibration, nu(3), and the overtone of the bending vibration. Sixty vibrational levels of the ground state with /l/ = 0 and l have been assigned, They could tie fitted by least squares to a simple matrix representation of the Fermi resonance that ignores the orbital angular momentum the interaction matrix element, as a fraction of the bending frequency, turns out to be larger than that in the "prototype" molecule, CO2. The two low-lying excited electronic states, (X) over tilde (2)Delta(3/2) at 830 cm(-1) and (W) over tilde (2)(1)Pi(3/2) at 2238 cm(-1), have very similar properties to the ground state. The energies of the excited states in the visible region bear a remarkable resemblance to those found in NiH (S, A. Kadavathu et al., 1991, J. Mol. Spectrosc. 147, 448-470). Again, the effects of Fermi resonance in them are large but those of vibronic coupling are surprisingly small. The most significant vibronic coupling occurs between the (A) over tilde (2)Delta(5/2) and (B) over tilde (2)Pi(3/2) states, which are separated by 79 cm(-1), an interval which is less than half the frequency of the bending vibration that couples them large numbers of vibronically induced bands appear in the excitation and dispersed emission spectra, but the splitting between (tie vibronic components of the bending fundamental of the (A) over tilde (2)Delta(5/2) state is only 6.988 cm(-1). Rotational perturbations are widespread in the (A) over tilde (2)Delta(5/2) state, particularly in the levels of the nu(3) (Ni-C stretching) progression, Vibrational assignments have been made on the basis of the Ni-58-Ni-60 isotope shifts at high resolution and the Franck-Condon patterns in dispersed emission spectra, Various weak unassigned bands, both in the excitation and the dispersed emission spectra, give evidence for the existence of at least three more excited electronic states which it has not been possible to characterize in detail. (C) 2002 Elsevier Science (USA)