Vibrational radiative cooling of isolated ${{\rm{C}}}_{4}^{-}$ and ${{\rm{C}}}_{6}^{-}

We have observed the storage-time dependence of the laser-induced electron detachment yields for the linear carbon cluster anions \({{\rm{C}}}_{4}^{-}\) and \({{\rm{C}}}_{6}^{-}\) stored in an electrostatic ion storage ring (TMU E-ring) with several laser wavelengths. The electron detachment yield reflects the decrease of the internal energy of the stored ions. We succeeded in obtaining the time evolution of the excitation energy distribution below the first dipole-allowed electronic excited energy E ex for \({{\rm{C}}}_{4}^{-}\) and \({{\rm{C}}}_{6}^{-}\), which was well consistent to the behavior explained by vibrational IR-radiative cooling.