The chemical and electronic structure of ultrathin molecular films of trimethylamine alane (TMAA), condensed in UHV at -100 degrees C, have been studied in the solid state, using both X-ray and ultraviolet photoelectron spectroscopy. The results are analyzed with the help of quantum chemical calculations at the ab initio Hartree-Fock 6-31G* level. Based upon the good agreement between theory and experiment, it is determined that clean, oxygen-free, condensed molecular solid films consist of the 2:1 adduct of TMAA, which was previously uncertain. In addition, based upon the electronic structure results, it is clear that the mechanism of the photodecomposition of TMAA can be explained in terms of the wavefunction of electrons photoexcited into the first unoccupied molecular orbital.