Ab initio methods have been used to predict the spectroscopic parameters for the ground (X (2)Pi(i)) and first (A (2)Sigma(+)) excited states of the unknown silicon halomethylidyne (SiCF, SiCCl, and SiCBr) free radicals. The predictive power of the chosen theoretical methods has been satisfactorily tested on the known SiCH radical. Calculations show that the linear Si=C-X species is the global minimum on the potential energy surface, with the bent X-Si=C isomer several thousand cm(-1) higher in energy. For the ground states, the geometries, vibrational frequencies, spin-orbit coupling constants, and Renner-Teller parameters have been predicted at several levels of theory with three different basis sets. These results can be used to generate a set of ground-state vibrational energy levels which may be useful in assigning the emission spectra of the radicals. The excited state geometries, vibrational frequencies, and excitation energies have also been calculated and the rotational contours of the 0(0)(0) bands have been simulated at medium resolution under jet-cooled conditions. These calculations have been employed in a successful search for the spectrum of the SiCCl radical.