Microsolvation of Salts in Water:Photoelectron Spectroscopy and Theoretical Studies of Size-Selected Salt-Water Clusters

【作者】 郑卫军；

【Author】 Weijun Zheng;Beijing National Laboratory for Molecular Sciences(BNLMS),Institute of Chemistry,Chinese Academy of Sciences;

【机构】 Beijing National Laboratory for Molecular Sciences(BNLMS),Institute of Chemistry,Chinese Academy of Sciences；

【摘要】 In order to understand the microsolvation of salts in water, we investigated a series of salt-water clusters using photoelectron spectroscopy. The structures of these clusters and their corresponding neutrals were investigated with ab initio calculations and confirmed by the photoelectron spectroscopy experiments. Our studies show that the SSIP type of structures start to appear at n=5 in Li I(H2O)n clusters. However, the separation of the Cs+-I-ion pair by water is insignificant in Cs I(H2O)n clusters. For neutral Na Cl(H2O)n, the CIP structures are dominant at n < 9. At n = 9-12, the CIP structures and SSIP structures of Na Cl(H2O)n are nearly degenerate in energy, coincident to the H2O:Na Cl molar ratio of Na Cl saturated solution and implying that the CIP and SSIP structures can coexist in concentrated solutions. For Li2SO4(H2O)n-cluster anions with n = 1–3, two kinds of isomers derived from the turtle-shaped and propeller-shaped structures of bare Li2SO4-were identified. These two kinds of isomers present similar structural and energetic features with increasing number of water molecules and thus are not distinguishable at n = 4–5. For the anionic Li2SO4(H2 O)n clusters, the water molecules prefer to firstly interact with one Li atom until fully coordinating it. While for the neutral Li2SO4(H2 O)n clusters, the water molecules interact with the two Li atoms alternately, therefore, show a pairwise solvation behavior. These results indicate that the structural variation and microsolvation in salt-water clusters are determined by the delicate balance between ion-ion, ion-water, and water-water interactions, which may have significant implications for the general understanding of salt effects in water solutions.更多还原

【Abstract】 In order to understand the microsolvation of salts in water, we investigated a series of salt-water clusters using photoelectron spectroscopy. The structures of these clusters and their corresponding neutrals were investigated with ab initio calculations and confirmed by the photoelectron spectroscopy experiments. Our studies show that the SSIP type of structures start to appear at n=5 in Li I(H2O)n clusters. However, the separation of the Cs+-I-ion pair by water is insignificant in Cs I(H2O)n clusters. For neutral Na Cl(H2O)n, the CIP structures are dominant at n < 9. At n = 9-12, the CIP structures and SSIP structures of Na Cl(H2O)n are nearly degenerate in energy, coincident to the H2O:Na Cl molar ratio of Na Cl saturated solution and implying that the CIP and SSIP structures can coexist in concentrated solutions. For Li2SO4(H2O)n-cluster anions with n = 1–3, two kinds of isomers derived from the turtle-shaped and propeller-shaped structures of bare Li2SO4-were identified. These two kinds of isomers present similar structural and energetic features with increasing number of water molecules and thus are not distinguishable at n = 4–5. For the anionic Li2SO4(H2 O)n clusters, the water molecules prefer to firstly interact with one Li atom until fully coordinating it. While for the neutral Li2SO4(H2 O)n clusters, the water molecules interact with the two Li atoms alternately, therefore, show a pairwise solvation behavior. These results indicate that the structural variation and microsolvation in salt-water clusters are determined by the delicate balance between ion-ion, ion-water, and water-water interactions, which may have significant implications for the general understanding of salt effects in water solutions.更多还原