Reaction and solvation of sodium in hydrogen bonded solvent clusters

Abstract

The reactive scattering of water clusters (H₂O)_n, n ≤ 160 and ammonia clusters (NH₃)_n, n ≤ 250 with 1 to 60 of sodium atoms is investigated. The water and ammonia cluster beams, respectively, are created in a pure supersonic expansion and cross an atmosphere of sodium vapor in a pickup cell. The reaction products are detected by photoionisation close to the threshold and mass analysed in a reflectron time-of-flight mass spectrometer. At low pickup pressures, sodium doped water and ammonia clusters are detected which reflect the correct size distribution of the pure cluster beams. At larger pickup pressures many sodium atoms are captured. In the case of ammonia thereby finally pure sodium clusters are produced, and the initial ammonia cluster is completely evaporated by the heat of formation of the formed sodium clusters. The water clusters, in contrast, react with the captured sodium until pure, even numbered sodium hydroxide clusters Na(NaOH)_m doped with one sodium atom and hydrogen molecules are formed. In this way the unique reaction mechanism observed and calculated for small systems is confirmed. The additional Na atom serves together with the solvent water molecules as catalyst for creating the reaction intermediate NaH.