We discuss rotational excitation of molecules by a pair of left and right circularly polarized laser pulses. The pulses are supposed to be short enough to avoid relaxation (femto- or picosecond), sufficiently intense to induce adiabatic evolution, and far-off-resonant, e.g. infrared. This technique has been demonstrated recently by Villeneuve {\em et al} [Phys. Rev. Lett. {\bf 85}, 542 (2000)] in rotational dissociation of molecules. In the present paper we analyze the properties of this technique by using the concepts of level crossing and adiabatic evolution. These allow us to derive analytically the conditions for efficient excitation. We analyse both the cases of red-to-blue and blue-to-red chirps and examine various initial conditions. Finally, we propose a novel technique, which can create superrotors by applying narrow pulses at particular level crossings.