The absorption and Raman spectra for nickel dimers in an argon matrix prepared by the mass-selected ion deposition technique have been measured. A weak dimer absorption band is centered around 480 nm. Resonance Raman spectra obtained from exciting into the dimer 480 nm band show a vibrational progression for which w_e=259.2(30) cm^-1 with w_ec_e=1.9(7) cm^-1. The dinickel Raman spectra are discussed in terms of isotopic shifts, as well as the changeover from d-d bonding to s-s bonding along the series Fe₂-->Cu₂.