  The translational motion of molecular ions can be effectively cooled
sympathetically to translational temperatures below 100 mK in ion traps through
Coulomb interactions with laser-cooled atomic ions. The ro-vibrational degrees
of freedom, however, are expected to be largely unaffected during translational
cooling. We have previously proposed schemes for cooling of the internal
degrees of freedom of such translationally cold but internally hot
heteronuclear diatomic ions in the simplest case of ^1-Sigma electronic ground
state molecules. Here we present a significant simplification of these schemes
and make a generalization to the most frequently encountered electronic ground
states of heteronuclear molecular ions: ^1-Sigma, ^2-Sigma, ^3-Sigma and ^2-Pi.
The schemes are relying on one or two laser driven transitions with the
possible inclusion of a tailored incoherent far infrared radiation field.
