REACTIVE SCATTERING OF SODIUM CLUSTERS WITH MOLECULAR-OXYGEN

The first reactive differential scattering study for atomic clusters i s reported. Oxidation of Na-x (x less than or equal to 8) with O-2 is investigated in a crossed beam apparatus. Sodium oxide (NanO, n less t han or equal to 4) and sodium dioxide (NanO2, n less than or equal to 6) are produced with a total reactive cross section from 50 to 80 Angs trom(2), depending on the cluster size. The excess energies for these reactions are estimated by an SCF type ab initio calculation and range from 0.5 to 5 eV. The large cross section may then be understood quan titatively in terms of a harpooning mechanism as a first step in the r eaction path. Angular distributions have been determined for the most abundant products, showing strong forward scattering. Two different sc hemes are discussed for the reaction: while the dioxides NanO2 may be formed by an evaporative cooling process from a highly excited collisi on complex, formation of NanO appears to originate from a direct proce ss. In both cases the experimental data suggest that most of the exoth ermicity remains in the reaction products.