  The vibrational quenching cross sections and corresponding low-temperature
rate constants for the v = 1 and v = 2 states of CN- colliding with He and Ar
atoms have been computed ab initio using new three dimensional potential energy
surfaces. Little work has so far been carried out on low-energy vibrationally
inelastic collisions for anions with neutral atoms. The cross sections and
rates calculated at energies and temperatures relevant for both ion traps and
astrochemical modelling, are found by the present calculations to be even
smaller than those of the similar C2- /He and C2-/Ar systems which are in turn
of the order of those existing for the collisions involving neutral diatom-atom
systems. The implications of our finding in the present case rather small
computed rate constants are discussed for their possible role in the dynamics
of molecular cooling and in the evolution of astrochemical modelling networks.
