Reactions of Ba Atoms with NO2, O3 and Cl2: Dynamic Consequences of the Divalent Nature of Barium

The role of the divalent nature of barium atoms in chemical reactivity was explored using crossed molecular beams. Angular and velocity distributions of products from reactions of Ba(1S) with NO2 and O3 indicate the existence of long lived collision intermediates despite very large reaction exothermicities. The existence of these intermediates results from barriers to transfer of the second electron necessary to form ground state products. Although BaO was the dominant product in both reactions, two previously unknown channels were observed: Ba + N02 → BaON + O and Ba + O3 → BaO2 + O. We obtained bond dissociation energies of D0(Ba–ON) = 270 ± 80 kJ/mol and D0(Ba – O2) = 500 ± 80 kJ/mol for these molecules. The dependence of the cross sections for the ion channels, Ba(1P) + Cl2 → Ba+ + Cl−2 and Ba(1P) + Cl2 → BaCl+ + Cl− on Ba(1P) orbital alignment and collision energy was used to probe the course of the reaction through intersections between the ionic and covalent potential energy surfaces.