The cluster isolated chemical reaction technique was used to investigate the reactivity of the Ba/CO2 and Ba/SF6 systems in the environment of Ar-approximate to 6000 clusters. The method was extended to document several aspects of the reactivity. Notably, mass spectrometry gives insight into the full reactivity of the system deposited on the clusters. Laser induced fluorescence (LIF) and chemiluminescence are also used as detection tools. Unexpectedly, we found that a single barium atom neither reacts with CO2 nor with SF6, at the cluster temperature (32 K). In contrast, the LIF results suggest the formation of a weakly bound covalent Ba ... CO2 complex. Finally, Ba-2 and larger barium aggregates react with CO2, and Ba-3 and larger aggregates react with SF6. The chemiluminescent products are Ba2O in the first case, and BaF in the second. These observations are rationalized on the ground of the harpoon model. (C) 1997 American Institute of Physics.