Abstract
We review the emission of molecular hydrogen (H[2]) in planetary nebulae (PNe) and we discuss the association between this emission and the bipolar morphology of the objects. We describe the energy levels of the hydrogen molecule, the main excitation mechanisms (shocks and fluorescence) and the ways of discrimination between the different excitation mechanisms. We propose another way of identification of the excitation mechanism based on H[2] kinematical studies. We present preliminary results of the H[2] kinematics we are conducting on a sample of five bipolar PNe. By means of this study we are able of identifying shocks as the main excitation mechanism of the H[2] emission lines in these objects. We have also estimated the masses of the H[2] gas in these PNe and the result implies that the progenitor's masses of these objects are larger than those of typical PNe progenitors.
