@misc{oai:ir.soken.ac.jp:00000271,
 author = {實方, 真臣 and サネカタ, マサオミ and SANEKATA, Masaomi},
 month = {2016-02-17, 2016-02-17},
 note = {1.Introduction. 
  Electrons and metal ions in fluids play important roles in many aspects of chemlcal phenomena and have been the subject of numerous investigations for many years. Although experimental and theoretical studies have attempted to understand the nature and the dynamics of solvation for these species, its mlcroscoplc aspect has not yet been fully understood Recently, advences in molecular beam technique open new approaches to a microscopic investigation of the excess electrons and metal ions in fluids. The clusters containing neutral metal atoms and/or their ions have found to be easily produced study of successively large clusters is analogous to modeling in a beam. The study of succesively large clusters is analogous to modeling  the process of solvation and provides us information on microscopic solvation.  
  The purpose of this study is to get insights into the electron delocalization, the formation of solvation shell, and the fundamental interactions among ions, solvent molecules, and electrons via the observation of the physical and chemical properties of the gas-phase clusters containing metal atoms and their ions as a function of number of solvent molecules. 
2. Photoionization processes of solvated alkali atom clusters. 
  Cesium atoms solvated with polar solvents, Cs(H2O)n,Cs(NH3)n, and Cs(CH3CN)n, are studied by onephoton ionization and time-of-flight mass spectroscopy. The solvated Cs atom clusters are produced by a pickup type cluster source. Ionization potentials of these clusters are determined by the observation of photoionization efficiency curves as a function of the laser photon energy. The ionization potentials of Cs(H2O)n and Cs(CH3CN)n are found to be constant for n>4 (3. 1eV) and n>12 (2.4eV), respectively, while that for Cs(NH3)n decreases monotonically with increasing n to a limit of 1.4eV, which coincides with the bulk value. These results are discussed in connection with the stability of solvated electrons in these polar solvents. Especially, the behavior of the ionization potentials for Cs(H20)n, which exhibit the bulk valuc only at n=4, is ascribed to the stabilization of an ion pair state; a spontaneous ionization of metal atom occurs even in the small clusters. 
3. Photodissociation processes of hydrated alkaline-earth metal ion clusters. 
  Ionic clusters are relevant to many chemical phenomena such as flame, catalysis, solvation, surfaces, and uncleation. In particular, the clusters containing metal ions have studied extensively, because these clusters play an important role for the reactions both in the gas-phasc and in solution. These ions are also observed as  the constituents of the upper/lower atmosphere. Ulntil now, most of the studies on the solvated clusters containing metal ions have been devoted to determining the successive hydration energies by high-pressure mass spectrometry, and collision induced dissociation and photodissociation. While the spectroscopic study of clusters as a specific function of cluster size can also play a crucial role in understanding the above phenomena, however, the experimental studies have been quite limited. 
  In order to get insights into energetics and dynamics of solvation, the photodissociation processes of the hydrated alkaline-earth metal ion clusters,M+ (H2O)n for M=Mg and Ca, are investigated using a reflectron type time-of-flight mass spectrometer. Since the alkaline-earth metal ions have an isoelectronic structure with alkali atoms, these systems include the same issue on the electron delocalization in clusters as mentioned in the previous section. Theph otodissociation spectra and the branching fractions of the photofragment ions are measured for the size-selected M+(H2O)n ions as a function of the photolysis energy. The time dependent photodissociation is also carried out for n=2. On the basis of these results, the electronic structure, the solvation shell, and the photodissociation processes of these clusters are discussed in relation in to the solvation in bulk fluids.  Photodissociation of Mg+(H2O)n for n=1-5. Photodissociation spectra of Mg+(H2O)n for n=1-5 are examined in the wavelength region from 250 to 720nm by monitoring the total yields of the fragment ions. The absorption bands exhibit redshifts as large as 17000cm-1 with respect to the 2P(3p)-2S(3s) resonance line of the free Mg+ ion and are explained by the shift of this transition as a result of hydration. The spectra also exhibit clear evolution of solvation shell closing at n=3, being consistent with the theoretical prediction. As for the larger clusters, the spectral features are almost the same as that for n=3. These results indicate that the effect of the second-shell waters on the electronic structure of the Mg+ ion is quite small. The mass spectra of the fragment ions show the existence of two dissociation processes: the evaporation of water molecules and the photoinduced intracluster reaction to produce the hydrated MgOH+ ion, MgOH+(H2O)n, with an H-atom elimination. The intracluster reaction is found to depend strongly on the cluster size and the photolysis wavelength. The energetics and dynamics of these dissociation processes are discussed in conjunction with the results of ab initio calculations. 
  Photodissociation of Ca+(H2O)n for n=1-6. The photodissociation of sizeselected Ca+(H2O)n ions are investigated for n=1-6. The photodissociation spectra are recorded in the wavelength region from 335 to 1440nm. The spectra for this entire series of clusters show large redshifts as large sa～18000cm-1 relative to the atomic resonance lines of Ca+ near 395nm. In contrast to Mg+ (H2O)n, the absorption bands redshift monotonically with increasing cluster size for n up to 6. This discrcpancy is attributed to the difference in the number of solvent molecules filling the first solvation shell, because of an sdo hybrization for the latter ion: The first shell of the Ca+(H2O)n may be filled at n～6. In the case of Ca+, the 2D(3d) state lies between the electronic ground 2s(4s) state and the 2P(4p) state. The electronic structures of these clusters are discussed including the mixing of these states. As in the Mg+ -H2O system, the dehydrogenation reactions to produce the hydrated CaOH+ ions are also observed for Ca+-H2O system. However the sizedependene of the reaction for Ca+(H2O)n is found to be different from that for Mg+(H2O)n. The results are discussed in relation to the electronic character of these cluster ions. 
4. Reaction of singly charged alkaline-earth metal ions with water clusters. 
  In the previous sections, they discussed the geometrical structure, electronic structure and reactivity of the M+(H2O)n clusters. In order to understand the solvation dynamics of metal ions, the investigation of the reaction between the metal ions and water clusters is also important. In the present study, they study the reactions of Mg+ and Ca+ ions with water clusters using the reflectron time of  flight mass spectrometer combined with the laser vaporization technique. Both the M+(H2O)n and MOH+(H2O)n-1(M=Mg and Ca) ions are found to form as the reaction products with characteristic size distribution: the latter ions are producced via an H-atom elimination reaction (oxidation of M+). As for the Mg+ ion, the Mg+(H2O)n ions are dominantly produced for 1<n<5 and n>15, while MgOH+ (H2O)n-1 are exclusively observed for 6 < n < 14 in the mass spectrum. The similar product distributions are also observed for Mg+-D2O, Ca+ H2O and Ca+ -D2O systems, though they are found to be affectcd by deuterium and metal substitutions. They also roexamine the photodissociation processes of the mass-selected Mg+(H2O)n(n=1 5)ions, in which the photoexcitation induces both the H -atom elimination reaction and the evaporation of water molecules. On the basis of these results, the first product switching at n=5 for Mg+(n=4 for Ca+) is ascribed to the difference in the successive hydration energies of the M+ and MOH+ ions. As for the second product switching, two possible mechanisms are proposed such as the stabilization of a Rydberg type ion-pair state and the involvement of a new product., application/pdf, 総研大甲第102号},
 title = {金属原子またはそのイオンを含むクラスターの微視的溶媒和過程に関する研究},
 year = {}
}