Near-equilibrium potential energy and dipole moment functions have been calculated for the linear mercury halide molecules HgCl2, HgBr2, and HgBrCl using highly correlated coupled cluster wave functions and large correlation consistent basis sets. After extrapolation to the complete basis set limit, additional corrections due to core-valence correlation and relativity were included in the final anharmonic potential energy functions (PESs). The fitted PESs and dipole moment functions were then used in variational calculations of the low-lying rovibrational band origins. Both the asymmetric stretch and symmetric bend fundamental bands are predicted to carry significant oscillator strength for all three species. A wide range of spectroscopic properties are accurately predicted, which should facilitate the observation of these species by high resolution spectroscopy. (C) 2003 American Institute of Physics.