A theoretical study of the binary titanium-carbon cations TiC2+ and Ti2C4+ has been carried out. The TiC2+ global minimum is a T- shaped C-2v-symmetric structure corresponding to a (2)A(2) electronic state, whereas the lowest-lying linear isomer lies about 20 kcal/mol higher in energy. In the case of Ti2C4+ the ground state corresponds to the B-4(u) state of an isomer where two TiC2 cyclic units are bonded through two Ti-C sides. Predictions for different molecular properties and for the IR spectra are provided. (c) 2006 Elsevier B.V. All rights reserved.