Kiyokazu Fuke

Photoionization studies of germanium and tin clusters in the energy region of 5.0–8.8 eV: Ionization potentials for Gen (n=2–57) and Snn (n=2–41)

Photoionization thresholds for Gen (n⩽57) and Snn (n⩽41) are examined by laser photoionization with detection by reflectron time-of-flight mass spectrometry. Stimulated Raman anti-Stokes scattering of narrow bandwidth 193, 248, and 266 nm radiation is used to produce ionization light sources in the vacuum ultraviolet region (200–141 nm). A very similar size dependence of the ionization potentials (IPs) is found for germanium and tin clusters with fewer than 12 atoms, featuring a major maximum at n=10. The rather high IP of Ge10 compared with its neighbors is consistent with the results of a photodissociation study of Gen+. We also find a rapid decrease in the IPs for Gen between n=15 and 26, which is very similar to that for silicon clusters reported in our previous paper. On the other hand, the IPs of medium size Snn (n=15–41) clusters are found to decrease slowly without such a gap. The remarkable difference in the size dependence of the IPs for the Sin, Gen, and Snn clusters is discussed in relation to...

Ab initio MO study of solvated negative alkali atom clusters: [M(H2O)n]− and [M(NH3)n]− (M Na and Li, n = 1−3)

Abstract The structures, stabilities and vertical electron detachment energies (VDEs) of [Na(H 2 O) n ] − , [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − ( n = 1−3) are investigated by the ab initio MO method at the correlated level. The Naue5f8H interactions and hydrogen bonds are important in [Na(H 2 O) n ] − , while the metal-N bonds become essential in stabilizing the [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − with increasing n . The size dependence of the VDEs of [Na(H 2 O) n ] − differs from that of [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − due to their structural features. In addition, the geometries and VDEs of [Li(H 2 O) n ] − ( n = 1−3) are predicted theoretically. The size dependence of their VDEs is similar to that of [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − rather than [Na(H 2 O) n ] − .

Photodissociation of Mg+(NH3) ion

Abstract Electronically excited states of Mg + (NH 3 ) are studied by photodissociation after mass selection. The dissociation spectrum shows relatively sharp vibronic transitions centered at about 28xa0000 and 36 000 cm −1 . These absorption bands are assigned to the 2 P – 2 S type transitions localized on the Mg + ion. In photodissociation, a photoinduced charge-transfer process to produce NH 3 + is observed in addition to evaporation and intracluster reaction processes to produce Mg + and MgNH 2 + ions, respectively. The mechanism for the production of these ions is discussed in terms of the predissociative and non-adiabatic interactions between the low-lying states.

Microscopic solvation process of single Li atom in small water clusters

Abstract We examine the photoelectron spectra of negatively-charged water clusters containing a Li atom, Li−(H2O)n (n⩽10), to reveal the hydration state of the Li atom in water clusters. The 2 S - and 2 P -type transitions of Li are found to be shifted to the lower electron binding energy with increasing cluster size up to n=4 and then shift back to higher binding energy for n⩾5. We discuss these results in relation to the spontaneous ionization of the Li atom and the formation of two-center ion-pair state, which is a counter part of hydrated electron.

Photodissociation and ab initio studies of Mg+(NH3)n, n=1–4: Electronic structure and photoinduced reaction

Photodissociation spectra of Mg+(NH3)nu200a(n=1–4) cluster ions are examined in the wavelength region of 240–1200 nm. From the comparison with the results of ab initio calculations for the structure and the excitation energies of these clusters, the observed absorption bands are assigned to the transitions derived from the 2P–2S transition of Mg+ ion. The extensive redshift of the observed spectra is ascribed to the formation of a one-center ion-pair state. In the photolysis of Mg+NH3, NH3+ and Mg+NH2 ions are produced via photoinduced charge transfer and intracluster reaction processes, respectively, in addition to the Mg+ ion generated by the evaporation of ammonia molecules. For n=2, both the intracluster reaction and evaporation are dominant decay processes, while the evaporation is the sole photodissociation channel for larger clusters. The branching fractions of these processes are found to depend strongly on the solvation number n and also on the photolysis wavelength. The energetics and the dynamics o...

Development of Novel Spectroscopic Magnet Combining Mass Spectroscopy With Nuclear Magnetic Resonance

We developed a superconducting magnet which is suitable for a novel spectroscopy. The methodology of the spectroscopy was suggested by Fuke. This enables to combine NMR (Nuclear Magnetic Resonance) spectroscopy with mass spectroscopy. In order to realize the spectroscopy, the magnet needs two homogeneous regions of 12 T and 4 T, respectively. The field gradient between two regions is required to be high enough. The coil structure is robust against high stress due to such an asymmetric field. The magnet is shielded actively and has a horizontal access room temperature bore of 155 mm diameter.

Multiphoton ionization and oxidation processes of Mg-ammonia clusters

Multiphoton ionization and oxidation processes of ammoniated magnesium clusters are investigated by the multiphoton ionization method with an intense femtosecond laser. In the photoionization of mass-selected Mg+ (NH3)n, evaporation dominates at lower laser intensity, while the oxidation reaction to produce H-atom elimination products, MgNH2+ (NH3)m, becomes predominant at higher intensity. In addition to these fragment ions, doubly-charged ions are observed for n > or = 2 at the laser intensity higher than 10(12) W cm(-2). We also examined the femtosecond pump probe experiments for Mg+ (NH3)4 by monitoring these reaction products. The lifetime of the first excited state is determined as 0.8 ps from the temporal profile of MgNH2+ (NH3)m. On the other hand, the time profile of the evaporation products exhibits a bleaching of the absorption, which gives the recovery time of the initial state as 1.2 ps. Multiphoton excitation of Mg(NH3)n with the femtosecond laser at 800 nm gives doubly-charged ions with n > 3 in addition to singly-charged cluster ions and H-atom elimination products such as MgNH2+ (NH3)m. The absence of small doubly-charged ions is ascribed to a charge reduction reaction followed by Coulomb explosion. On the basis of these results, the dynamics of the solvation and oxidation reaction processes of Mg(NH3)n is discussed.