  We present an opto-electrical cooling scheme for polar molecules based on a
Sisyphus-type cooling cycle in suitably tailored electric trapping fields.
Dissipation is provided by spontaneous vibrational decay in a closed level
scheme found in symmetric-top rotors comprising six low-field-seeking
rovibrational states. A generic trap design is presented. Suitable molecules
are identified with vibrational decay rates on the order of 100Hz. A simulation
of the cooling process shows that the molecular temperature can be reduced from
1K to 1mK in approximately 10s. The molecules remain electrically trapped
during this time, indicating that the ultracold regime can be reached in an
experimentally feasible scheme.
