This thesis builds on the spectroscopy of NiH established in the late 1980s and early 1990s, principally by Pr. R. W. Field's group at MIT. Experimental measurements significantly extend earlier work, both in field-free and Zeeman spectroscopy. The NiH radical is obtained with a room-temperature metal-hydride discharge source (310 K). Radicals formed in the discharge are excited by a single-mode, continuous wave dye laser and can be conveniently studied either in laser excitation or in dispersed fluorescence. A magnetic circuit with permanent magnets (NdFeB) provides a static magnetic field (0.4 – 0.9 T). In the field-free regime, Fourier transform resolved fluorescence spectra have extended the range of observations up to 6000 cm-1 above v=0 of the electronic ground state, for 58NiH and 60NiH. Energies are modeled with an effective Hamiltonien matrix using the 3d9 supermultiplet formalism developed by Field's group. Zeeman measurements have focused mainly on the range of states studied by including transitions involving the Ω=3/2 excited states. Effective Landé factors have been determined for individual ro-vibrational levels of low-lying and excited states of 58NiH. The unusual J-dependence of the Landé factors obtained for low-lying states are explained by the 3d9 supermultiplet model, quantifying the extent of spin-orbit mixing present in the lower states. The transitions are of potential astrophysical interest since several transition metal hydrides have been observed in the spectra of cool stars and sunspots.
