Molecular Adsorption-Desorption Reactions of Ammonia on Alkali Halide Clusters and Nanocrystals

Abstract

The initial adsorption of ammonia molecules (NH3) on larger alkali halide clusters and small nanocrystals (mainly NaF) has been investigated by flow-reactor methods as a function of cluster size and temperature.An analysis of the strong size-dependent reactivity of positively-charged NaF clusters, along with their computed structures, indicates that a particular type of defect in the nanocrystal structure facilitates adsorption. This defect is formed by removing an ion-pair from adjoining face and internal sites of a perfect crystallite, creating a basket-like opening. KF nanocrystals show very similar reactivity patterns, reflecting their corresponding structures, but LiF clusters follow a different pattern. It was established that NH3 adsorption on preformed NaF nanocrystals takes place under equilibrium conditions. The equilibrium constant for initial adsorptiondesorption increases with decreasing temperature (250-340 K) and allows one to derive heats of N H 3 adsorption near 0.2 eV for the more reactive (defective) nanocrystals. The much lower reactivity of negatively-charged clusters is ascribed to an additional kinetic-dynamic barrier to adsorption.

Compact Non-Rock-Salt Structures in Sodium Fluoride Cluster Ions at Specific Sizes Revealed by Ion Mobility Mass Spectrometry

“…Monocationic ions of sodium fluoride clusters have been observed as a stable series of Na n F n –1 + in a mass spectrum because Na + cations and F – anions make ionic bonds alternately in the cluster ions. In the past several decades, structures of Na n F n –1 + cluster ions were correlated with the well-known rock-salt type structures of the bulk crystal of sodium fluoride. − In the mass spectrum, intensity anomalies (magic numbers) were observed at n = 5, 14, 23, 32, 38, 53, and 63 . Structures of these alkali halide cluster cations were assigned to cuboids, where the 2 n – 1 ions occupy the j × k × l lattice sites .…”

Photodissociation of Sodium Iodide Clusters Doped with Small Hydrocarbons

“…The investigation of alkali halide clusters in the gas phase was pioneered by Whetten and Martin and further followed by other authors . Particularly well studied is the adsorption of ammonia and water to a variety of alkali halide species. Drewello and co‐workers studied the stability of salt clusters attached to crown ether decorated phthalocyanines .…”

“…Besides chloride, other halide ions like iodide are presenti n traces in sea-salt aerosols, and may alter their chemistry and photochemistry.T he investigation of alkali halide clusters in the gas phase was pioneered by Whetten and Martin and further followed by other authors. [14][15][16][17] Particularly well studied is the adsorption of ammonia [18,19] and water [20][21][22][23][24][25] to av ariety of alkali halide species. Drewello and co-workers studied the stability of salt clusters attached to crown ether decorated phthalocyanines.…”

Infrared multiple photon dissociation of cesium iodide clusters doped with mono-, di- and triglycine

“…Alkali halide clusters in the gas phase were extensively studied by Whetten, 36 Martin, 27 Whetten et al 38 and Lintuluoto. 39 Especially, the adsorption of ammonia 40,41 and water [42][43][44][45][46] to various alkali halides was investigated by several groups. The collision cross section of sodium iodide clusters was studied by Ouyang et al 47 using mobility measurements, while Blades et al 48 investigated the hydration energy of Na 2 I þ .…”

“…38 and Lintuluoto. 39 Especially, the adsorption of ammonia 40,41 and water 42–46 to various alkali halides was investigated by several groups. The collision cross section of sodium iodide clusters was studied by Ouyang et al.…”