AMMONIA ALANE

Ab initio studies employing basis sets approaching triple-zeta plus double-polarization plus f function quality are reported for AlH3 NH3, AlH3, and NH3. The self-consistent-field method was employed for all basis sets; the single and double excitation configuration interaction and the comparable coupled-cluster methods were utilized with a double-zeta plus polarization functions basis set. The dissociation energy of AlH3 NH3 is predicted to be 26 kcal/mol after correcting for zero-point vibrational energy, in qualitative agreement with the rough estimate of 30 kcal/mol by Haaland for Al-N bond strengths. In keeping with the dative nature of the Al-N bond, the AlH3 and NH3 moieties do not undergo larger changes upon the formation of AlH3 NH3. The resemblance of AlH3 NH3 to the related compound BH3 NH3 is quite strong. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities, atomic charges, and dipole moment of ammonia alane are reported.