  We present a complete study of the H2 infrared emission, including the pure
rotational lines, of the proto Planetary Nebulae CRL 618 with the ISO SWS. A
large number of lines are detected. The analysis of our observations shows: (i)
an OTP ratio very different from the classical value of 3, probably around
1.76-1.87; (ii) a stratification of the emitting region, and more precisely
different regions of emission, plausibly located in the lobes, in an
intermediate zone, and close to the torus; (iii) different excitation
mechanisms, collisions and fluorescence.
