Radiative cooling of H3O+ and its deuterated isotopologues
  In conjunction with ab initio potential energy and dipole moment surfaces for
the electronic ground state, we have made a theoretical study of the radiative
lifetimes for the hydronium ion H$_3$O$^{+}$ and its deuterated isotopologues.
We compute the ro-vibrational energy levels and their associated wavefunctions
together with Einstein coefficients for the electric dipole transitions. A
detailed analysis of the stability of the ro-vibrational states have been
carried out and the longest-living states of the hydronium ions have been
identified. We report estimated radiative lifetimes and cooling functions for
temperatures $<$ 200 K. A number of long-living meta-stable states are
identified, capable of population trapping.
