Showing papers by "Hiroshi Sekiya published in 2007"

Infrared spectroscopy of Cu+(H2O)(n) and Ag+(H2O)(n): coordination and solvation of noble-metal ions.

Abstract: M(+)(H(2)O)(n) and M(+)(H(2)O)(n)Ar ions (M=Cu and Ag) are studied for exploring coordination and solvation structures of noble-metal ions These species are produced in a laser-vaporization cluster source and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region using a triple quadrupole mass spectrometer Density functional theory calculations are also carried out for analyzing the experimental IR spectra Partially resolved rotational structure observed in the spectrum of Ag(+)(H(2)O)(1) x Ar indicates that the complex is quasilinear in an Ar-Ag(+)-O configuration with the H atoms symmetrically displaced off axis The spectra of the Ar-tagged M(+)(H(2)O)(2) are consistent with twofold coordination with a linear O-M(+)-O arrangement for these ions, which is stabilized by the s-d hybridization in M(+) Hydrogen bonding between H(2)O molecules is absent in Ag(+)(H(2)O)(3) x Ar but detected in Cu(+)(H(2)O)(3) x Ar through characteristic changes in the position and intensity of the OH-stretch transitions The third H(2)O attaches directly to Ag(+) in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu(+) The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag(+), in contrast to the extensive 4s-3d hybridization in Cu(+) which retains the dicoordination This is most likely because the s-d energy gap of Ag(+) is much larger than that of Cu(+) The fourth H(2)O occupies the second shells of the tricoordinated Ag(+) and the dicoordinated Cu(+), as extensive hydrogen bonding is observed in M(+)(H(2)O)(4) x Ar Interestingly, the Ag(+)(H(2)O)(4) x Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag(+)(H(2)O)(3) x Ar but revived at n=4 Size dependent variations in the spectra of Cu(+)(H(2)O)(n) for n=5-7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu(+)(H(2)O)(2) subunit is surrounded by four H(2)O molecules The gas-phase coordination number of Cu(+) is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes

Cooperative triple-proton/hydrogen atom relay in 7-azaindole(CH3OH)2 in the gas phase: remarkable change in the reaction mechanism from vibrational-mode specific to statistical fashion with increasing internal energy.

Abstract: The 7-azaindole-methanol 1:2 cluster [7AI(CH3OH)2] undergoes excited-state triple-proton/hydrogen atom transfer (ESTPT/HT) along the hydrogen-bonded network in the gas phase. The measurements of the resonance-enhanced multiphoton ionization (REMPI) spectra of 7AI(CH3OH)2-dn (n = 0−3), where subscript n indicates the number of deuterium, and the fluorescence excitation spectrum of 7AI(CH3OH)2-d0 allowed us to investigate the ESTPT/HT dynamics. By comparing the intensity ratios of the vibronic bands between 7AI(CH3OH)2-d0 and 7AI(CH3OH)2-d3 in REMPI spectra, we obtained the lower limit of an acceleration factor (falow) of 7AI(CH3OH)2-d0, which is the ratio of the reaction rate for the excitation of a vibronic state to that of the zero-point state in S1. The falow values are 2.7 ± 0.83 and 4.0 ± 1.2 for an in-phase intermolecular stretching vibration (σ1) and its overtone (2σ1) observed at 181 cm-1 and 359 cm-1 in the excitation spectrum, respectively, while that of the vibration (ν2/σ1 or ν3/σ1) at 228 cm-1...

Coordination and solvation of noble metal ions: Infrared spectroscopy of Ag+(H2O)n

Abstract: Vibrational spectra of mass-selected Ag+(H2O)n ions are measured by infrared photodissociation spectroscopy and analyzed with the aid of density functional theory calculations. Hydrogen bonding between H2O molecules is found to be absent for cold Ag+(H2O)3, but detected for Ag+(H2O)4 through characteristic changes in the position and intensity of OH-stretching transitions. The third H2O coordinates directly to Ag+, but the fourth H2O prefers solvation through hydrogen bonding. The preference of the tri-coordinated form is attributed to the inefficient 5s–4d hybridization in Ag+, in contrast to the efficient 4s–3d hybridization in Cu+. For Ag+(H2O)4, however, di-coordinated isomers are identified in addition to the tri-coordinated one.

Coordination and solvation of copper ion: infrared photodissociation spectroscopy of Cu+(NH3)n (n = 3–8)

Abstract: Coordination and solvation structures of the Cu+(NH3)n ions with n = 3–8 are studied by infrared photodissociation spectroscopy in the NH-stretch region with the aid of density functional theory calculations. Hydrogen bonding between NH3 molecules is absent for n = 3, indicating that all NH3 molecules are bonded directly to Cu+ in a tri-coordinated form. The first sign of hydrogen bonding is detected at n = 4 through frequency reduction and intensity enhancement of the infrared transitions, implying that at least one NH3 molecule is placed in the second solvation shell. The spectra of n = 4 and 5 suggest the coexistence of multiple isomers, which have different coordination numbers (2, 3, and 4) or different types of hydrogen-bonding configurations. With increasing n, however, the di-coordinated isomer is of growing importance until becoming predominant at n = 8. These results signify a strong tendency of Cu+ to adopt the twofold linear coordination, as in the case of Cu+(H2O)n.