Five low-lying (T-e < 2200 cm(-1)) electronic states of NiI have been observed using single vibronic level (SVL) emission spectroscopy, via three hitherto unobserved band systems in the range 21 150-22 410 cm (1). In addition to the previously characterized X-2 Delta(5/2) and A(2)Pi(3/2) states, the X-2 Delta(3/2), A(2)Pi(1/2), and B-2 Sigma(+)(1/2) states have been observed for the first time. The emission spectra yield term energies and vibrational constants that are in excellent agreement with recent ab initio calculations. A number of perturbations in the vibrational level structure can be identified and are attributed to homogenous interactions under the selection rule Delta Omega = 0. (c) 2010 Elsevier B.V. All rights reserved.