Effect of impurity chloride ions on equilibrium and nonequilibrium ion emission from crystalline BaF2

Thermal emission of positive ions from the exposed {111} face of a BaF 2 single crystal and from a crystalline BaF 2 sample placed in an effusion cell is studied by mass spectrometry between 980 and 1400 K. In both cases,BaCl + ions are detected, as well as BaF + and Ba 2 F + 3 + ions. The effect of impurity chloride ions on the emission efficiencies and relative intensities of the BaF + and Ba 2 F + 3 ions is analyzed. The enthalpy of formation of the cluster ion is refined to be Δ f H 0 (Ba 2 F + 3 , g, 0 K) = -911 ′ 20 kJ mol - 1 .