Dissociation energies of the molecules Bcl and Bcl⁺

The molecule Bcl was generated by chlorination of B(s) with both MgCl₂ and SrCl₂ in a heated effusive beam source, and identified by mass spectrometry. Gaseous equilibria in the B–Mg–Cl and B–Sr–Cl systems were studied in the regions 1350–1600 K and 1760–1830 K, respectively, and the dissociation energy D₀°(Bcl)=121.3±1.1 kcal mol⁻¹ (5.26±0.05 eV) was derived from thermochemical analysis. When compared with a dissociation limit derived from a short upper state extrapolation, this result indicates a potential hump of about 6 kcal mol⁻¹ in the A ¹Π state of Bcl. Electron impact measurements yielded an ionization potential of 10.03±0.10 eV for Bcl, which can be used to evaluate D₀°(Bcl⁺)=81.4±2.6 kcal mol⁻¹ (3.53±0.11 eV). Other values in the literature, some of which differ considerably from the new results, are discussed.