We report photoelectron spectra of the MC3- clusters for M=Sc, V, Cr, Mn, Fe, Co, and Ni at two photon energies, 355 and 266 nm. Vibrational structure is resolved for the ground and excited state detachment transitions for all the clusters except for CoC3- and NiC3-. Electron affinity (EA) and vibrational frequencies for the MC3 clusters are obtained. Complicated low-lying excited state features are observed for all the species. We find that the trend of the EA across the 3d series for the MC3 clusters is similar to that of the MC2 species. The vibrational frequency is found to increase from ScC3 to TiC3 and then decreases monotonically to the right of the 3d series. Preliminary density functional theory calculations are performed on all the MC3 and MC3- clusters at several initial geometries and spin multiplicities. We find that the ground states of all the MC3 and MC3- species have C-2v ring structures. The calculated M-C stretching frequency for all the MC3 species is in good agreement with the experimental measurement, lending credence to the obtained C-2v structure. (C) 2000 American Institute of Physics. [S0021-9606(00)00308-1].