  The dicarbon molecular anion is currently of interest as a candidate for
laser cooling due to its electronic structure and favorable branching ratios to
the ground electronic and vibrational states. Helium has been proposed as a
buffer gas to cool the molecule's internal motion. We calculate the cross
sections and corresponding rates for rovibrational inelastic collisions of the
dicarbon anion with He, and also with Ne and Ar, on three-dimensional ab initio
potential energy surfaces using quantum scattering theory. The rates for
vibrational quenching with He and Ne are very small and are similar to those
for small neutral molecules in collision with helium. The quenching rates for
Ar, however, are far larger than those with the other noble gases, suggesting
that this may be a more suitable gas for driving vibrational quenching in
traps. The implications of these results for laser cooling of the dicarbon
anion are discussed.
