We report the absorption, resonance Raman, and excitation spectra of mass selected cerium, praseodymium, and neodymium dimers in argon matrices. Absorption bands were found for each sample. The excitation profiles give more sensitive detail and resemble absorption spectra. Resonance Raman spectra give single progressions for which Ce-2: omega(e)=245.4 +/- 4.2 cm(-1), Pr-2: omega(e)=244.9 +/- 1.2 cm(-1), and Nd-2: omega(e)=148.0 +/- 1.9 cm(-1), omega(e)x(e)=0.7 +/- 0.4 cm(-1). Comparison among lanthanide dimers is discussed.