| Description: | A very important aspect in understanding planetformation is the characterization of the disk chemical composition in the region where planets are expected to form. It is only very recent that near and mid infrared observations of simple organic molecules, water and OH have been reported in T Tauri disks at distance 0.5-5 AU from the central star (Carr & Najita 2008; Salyk et al. 2008). The LTE models in these papers show that significant column densities of molecular species are present in the inner disk atmospheres. However, a more complete picture requires a better understanding of the chemistry and non-thermal excitation processes. In the talk, I will first analyze a number of physical processes that can affect the abundance of water in the warm part of the disk atmosphere (T > 200-300 K). Then I will focus on the non-thermal excitation processes of H2O, and show that these are important to understand the radial extent of its observed emission.
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