  The frictional heating by ion-neutral drift is calculated and its effect on
isobaric thermal instability is carried out. Ambipolar drift heating of
one-dimensional self-gravitating magnetized molecular slab is used under the
assumptions of quasi-magnetohydrostatic and local ionization equilibrium. We
see that ambipolar drift heating is inversely proportional to density and its
value in some regions of the slab can be significantly larger than the average
heating rates of cosmic rays and turbulent motions. The results show that the
isobaric thermal instability can occur in some regions of the slab; therefore
it may produce the slab fragmentation and formation of the AU-scale
condensations.
