===================================================================== ==> In this proposal, more time is being requested for MMEIXNER.PROP_AFS. ==> This proposal requests an upgrade from Priority 3 for MMEIXNER.PROP_AFS. ===================================================================== During the last stages of its evolution, low mass stars (<8 Msol) loose about 1 Msol in the form of a cool, low velocity (10 km/s) molecular wind on the Asymptotic Giant Branch (AGB). This phase is thought to end with a burst of increasing mass loss rate (the "superwind") which largely exhausts the star. The star then moves to the left in the HR diagram (the proto- planetary nebula phase, PPN). Once the central star becomes hot enough, the still expanding AGB wind will be ionized. At some point during its evolution, the central star will start losing mass in a fast (100-1000 km/s) but low density wind. This fast wind will drive fast shocks into the AGB wind. The interaction of these winds and the hardening of the UV radiation field will shape the resulting planetary nebula. Understanding this mass loss process and its evolution during the AGB, PPN and PN phases is a key problem within astrophysics because most of interstellar gas and dust originates from these stellar sources. Here, we propose high resolution spectroscopy of far-infrared atomic fine structure lines in IRAS 22272+5435 (PPN), Hb 12 (PN), and BD 30+3639 (PN). IRAS 22272+5435 has been detected in the [CII] 158 um line in the central programme and our proposed observations follow up on this important discovery. Hb 12 is the classical example of a PNe with a photodissociation region. BD 30+3639 has unusually high velocity molecular gas out flow suggestive of shocks. In all three cases, our proposed observations of the far-infrared atomic fine structure lines will provide information on the relative importance of photodissociation and shocks in these objects.