Reactions of Sodium Clusters with Water Clusters

In a crossed molecular beam experiment, the reactive scattering of sodium clusters Na n ( n ⩽ 21) with water clusters (H 2 O) m ( m ⩽ 40) is investigated. By measuring the angular and the velocity distributions of the scattered reaction products, direct information on the reaction mechanisms is obtained. The sodium clusters are generated in a supersonic expansion of sodium vapor from an oven with a refilling system with argon carrier gas. The products are detected by photoionization at wavelengths of 308 and 355 nm and mass analyzed in a time-of-flight mass spectrometer (TOF-MS). In addition, a fast chopper with a pseudorandom sequence modulating the sodium cluster beam allows us to determine at the same time the velocity distributions of the products. The scattering of Na clusters with H 2 O clusters shows only one series of reaction products, that is, solvated sodium atoms Na(H 2 O) m ( m ⩽ 32) with maximum intensities at m = 4, 5, 6. For all products, the measured angular and velocity distributions exhibit the formation of a complex that is stabilized by isotropic evaporation of water molecules. The detected products have low translational energy. Products containing NaOH have not been observed.