MASS-SPECTROMETRIC MEASUREMENT OF DISSOCIATION ENERGIES OF BEC1 AND BEC12

A mass spectrometer was used to study gaseous equilibria in the Be-Al-Cl system by passing HCl (g) over a Be-Al mixture in a Knudsen cell molecular source. For the reactions Be(g)+AlCl(g)= BeCl(g)+ Al(g) and Be(g)+BeCl 2(g) = 2 BeCl(g), ΔH298 values of 26.2±2 and 36.1±2 kcal, respectively, are derived. Also, the sublimation of BeCl2 was studied by torsion-effusion and mass-spectrometric techniques, from which the heat of sublimation ΔH298=32. 5±0.5 kcal/mole is derived for β-BeCl2. These data yield the dissociation energies D0°(BeCl) = 91.9 kcal (3.98 eV) and D0° (BeCl2) = 219.4 kcal (9.51 eV). The results are discussed briefly in terms of the chemical bonding.