Keizo Tsukamoto

Photoionization of clusters of Cs atoms solvated with H2O, NH3 and CH3CN

Abstract Cesium atoms solvated with polar solvents, Cs(H2O)n, Cs(NH3)n and Cs(CH3CN)n, are studied by one-photon ionization and time-of-flight mass spectroscopy. The ionization potentials of Cs(H2O)n and Cs(CH3CN)n are found to be constant for n ⩾ 4 (3.1 eV) and n ⩾ 12 (2.4 eV), respectively, while that for Cs(NH3)n decreases monotonically with increasing n to a limit of 1.4 eV, which coincides with the bulk value. Enhanced stability at n = 20 is also observed for the Cs(H2O)n clusters. These features are discussed in connection with the stability of the excess electrons in these solvents.

Heterogeneous two-dimensional nucleation and growth kinetics

A kinetic model is developed to describe the growth of crystals under the influence of foreign particles in terms of heterogeneous two-dimensional nucleation. In the context of this model, the free energy barrier of two-dimensional nucleation in the presence of foreign particles and the kinetics for the nucleation and growth are examined theoretically. It follows that the contact angle, size and density of adsorbed foreign particles play a crucial role in controling the 2D nucleation barrier and growth kinetics. Based on our model, many crucial experimental findings, such as dust-induced surface roughening and the various kinetics of dislocation-free growth, are properly interpreted. The promotion effect of foreign particles on crystal growth is also analyzed from the view of designing additives. To our knowledge, this is the first systematic consideration of effects of foreign particles on the 2D nucleation process and growth kinetics, and the model generally covers both heterogeneous and conventional ho...

Electronic structure and reactivity of Mg+(H2O)n cluster ions

Electronically excited states of magnesium-water cluster ions, Mg+(H2O)n,n=1–5, are studied by photodissociation after mass selection. The observed photodissociation spectra are assigned to the2P–2S type transitions localized on the Mg+ ion with the aid of ab initio CI calculations. In addition to evaporation of water molecules, photoinduced intracluster reaction to produce MgOH+(H2O)n is found to occur efficiently, with pronounced size dependence. The intriguing features observed in the mass spectrum of nascent cluster ions are discussed in relation to the stepwise solvation of this reaction.

Picosecond measurements of the vibrationally resolved proton‐transfer rate of the jet‐cooled 1‐azacarbazole dimer

Proton‐transfer reaction (PTR) of the jet‐cooled 1‐azacarbazole (1‐AC) dimer has been studied by directly measuring, in real time, the fluorescence intensity from the precursor dimer and from the tautomer formed in the excited‐state reaction process after exciting various intermolecular vibrational levels of the dimer. For the vibrational levels of the 1‐AC dimer examined here, PTR is found to be predominant in the overall decay process. The rate of PTR is strongly dependent on the vibrational mode and is enhanced pronouncedly by excitation of the intermolecular symmetric‐stretching vibration in the hydrogen bond.

PHOTOELECTRON SPECTROSCOPY OF MASS-SELECTED METAL-WATER CLUSTER NEGATIVE IONS: Cu−(H2O)n AND Na−(H2O)n

The electronic structures of hydrated metal-atom clusters have been investigated by negative-ion photoelectron spectroscopy. We have obtained the photoelectron spectra of Cu−(H2O)n with n=0−4 and Na−(H2O)n with n=0−12. For the former clusters, we also detected the electron detachment from the CuOH−(H2O)n−1 which coexists with Cu−(H2O)n. The observed bands for both Cu−(H2O)n and Na−(H2O)n were all assigned to the transitions to the states originating in those of the metal atoms, which are shifted as a result of hydration. This result implies that the ground states of the neutral clusters still have a one-center character at the size range examined. In contrast, for the Na–water clusters, increasing character of the Rydberg-type ion-pair state in the negative-ion state is suggested from the vertical-detachment-energy dependence on the solvent number.

Photoionization of small silicon clusters: ionization potentials for Si2 to Si40

Photoionization thresholds of Sin (n=2−40) were examined by vacuum UV radiation (5.7–8.5 eV) generated by stimulated Raman scattering of narrow-bandwidth 193-nm radiation in high pressure hydrogen and deuterium gases. A strong threshold energy dependence on cluster size is observed, featuring major maxima at 10 and 20. The magic behavior atn=10 is consistent with the results of the photofragmentation and CID experiments reported previously.

Photoionization and photodissociation studies on aluminum-water clusters and their ions

Clusters of aluminum atoms solvated with water molecules, Al(H2O)n, have been studied by one-photon ionization and time-of-flight mass spectroscopy. Characteristic feature is observed in the photoionization mass spectrum: The intensities of the product Al+(H2O)n ions are about one order of magnitude larger forn≤4 than forn≥5. The ionization potentials are determined forn up to 4. The obtained results are discussed in connection with the recent theoretical works. The photodissociation spectroscopy has also been applied to the Al+(H2O)n ions withn=1−10. The observed spectra are ascribed to the transition localized on the Al+ ion on the analogy of the results of Mg+(H2O)n photodissociation. The dissociation dynamics is also discussed from the fragmentation pattern with the aid of the recent theoretical work on the structure and stability of these ions.

Correlation between Electronic Shell Structure and Inertness of Cun+ toward O2 Adsorption at n = 15, 21, 41, and 49

The inertness of metal clusters in air is important for their application to novel materials and catalysts. The adsorption reactivity of copper clusters with O2 has been discussed in connection with the electronic structure of clusters because of its importance in electron transfer from the cluster to O2. Mass spectrometry was used to observe the reaction of Cu n+ + O2 ( n = 13-60) in the gas phase. For O2 adsorption on Cu n+, the relative rate constants of the n = 15, 21, 41, and 49 clusters were clearly lower than those with other n. Theoretical calculations indicated that the inertness of Cu15+ with 14 valence electrons was related to the large HOMO-LUMO gap predicted for the oblate Cu15+ structure. The Clemenger-Nilsson model was used to predict that the electronic subshell of oblate Cu49+ with 48 electrons was closed. This electronic shell closing of Cu49+ corresponds to the inertness for O2 adsorption.

Photoionization of Solvated Cs Atoms

Cesium atoms solvated by polar molecules are studied by one-photon ionization and time-of-flight mass spectroscopy. Ionization potentials (IPs) of Cs(H2O)n and Cs(CH3CN)n are found to be constant for n ≧ 4 (3.1 eV) and n ≧ 12 (2.4 eV), respectively, while the IPs for Cs(NH3)n and Cs(CH3OH)n decrease monotonically with increasing n. Cs(NH3)n gives a limit value of 1.4 eV, which coincides with the bulk value. Enhanced stability at n=20 is also observed for the Cs(H2O)n clusters. These features are discussed in connection with the structure of the cluster and the stability of the excess electrons in the condensed phase.