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), ${\mathrm{\Delta H}}_{298}$ 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 ${\mathrm{\Delta H}}_{298}\text{\hspace{0.17em}=\hspace{0.17em}32.5\hspace{0.17em}±\hspace{0.17em}0.5}\mathrm{kcal}/\mathrm{mole}$ is derived for β‐BeCl₂. These data yield the dissociation energies $D_0\mathrm{°(}\mathrm{BeCl}\text{)\hspace{0.17em}=\hspace{0.17em}91.9}\mathrm{kcal}$ (3.98 eV) and $D_0\mathrm{°(}{\mathrm{BeCl}}_2\text{)\hspace{0.17em}=\hspace{0.17em}219.4}\mathrm{kcal}$ (9.51 eV). The results are discussed briefly in terms of the chemical bonding.