Mass-Spectrometric Measurement of the Dissociation Energies of BeCl and BeCl2

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) + BeCl2(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.