1999A&A...348L..17W

The levitation of the outer atmospheres of AGB stars by pulsations is proposed as possible mechanism to form ``warm molecular layers''. We compare the amounts of CO, H₂O, CO₂ and SO₂ molecules found in an oxygen-rich dynamical model atmosphere with the values derived from recent ISO observations. In the model, the molecules are present in a layered structure behind shock waves which leads to a substantial increase of the column densities in comparison with static models. By additional non-LTE investigations, we calculate the vibrational and rotational excitation temperatures of these molecules and discuss the respective deviations from the kinetic gas temperature in view of the interpretation of the observations.