Thermodynamic study of the gaseous molecules Al2N, AlN, and Al2N2 by Knudsen cell mass spectrometry

The Knudsen effusion mass spectrometric method has been employed to measure the equilibrium partial pressures of the Al2N molecule over the AlN-Au-graphite system. Theoretical computations were carried out to determine the structure, molecular parameters, and thermodynamic properties of Al2N. The partial pressures have been combined with the calculated thermal functions to determine the atomization enthalpy, Delta H-a(0)o, and enthalpy of formation, Delta H-f(298.15)o, in kJ mol(-1), of 783.2 +/- 15 and 342.7 +/- 15 for Al2N, respectively. Upper values for the dissociation energy of AlN, D-0(o)(AlN,g)less than or equal to 368 +/- 15 kJ mol(-1), and for the atomization enthalpy of Al2N2, Delta H-a(0)o(Al2N2,g)less than or equal to 1402 kJ mol(-1) have been obtained. These results are discussed and compared with recent theoretical literature values. (C) 2000 American Institute of Physics. [S0021-9606(00)01448-3].