The potential energy curves of Br cations interacting With rare gas (RG = He-Ar) atoms are calculated employing the RCCSD(T) technique for the non-spin-orbit states, with spin-orbit coupling being included analytically, using an atoms-in-molecule approach. The curves are calculated employing large basis sets extrapolated to the complete basis set limit, and the energies are corrected for basis set superposition error. Comparison is made to the limited potentials available previously. Gaseous ion mobilities are obtained using the potential energy curves of the states of the complex that correlate to the Br+((3)Pj degrees) + RG asymptotes. Excellent agreement is obtained with the experimental data in He; however, the experimental error bars are Such that we are unable to determine which spin-orbit state(s) are present in the mobility measurements. Finally, a high-resolution photoelectron spectrum is simulated for the ionization of Br-Ar.