No abstract

Structures of methanol molecules chemisorbed on cobalt cluster ions, Co(n)(+) (n=2-6), were investigated by infrared photodissociation (IR-PD) spectroscopy in the wavenumber range of 3400-4000 cm(-1). All the IR-PD spectra measured exhibit an intense peak in the region of the OH stretching vibration. In the IR-PD spectra of Co(2)(+)(CH(3)OH)(2,3) and Co(3)(+)(CH(3)OH)(3), weak peaks were observed additionally in the vicinity of 3000 cm(-1), being assignable to the CH stretching vibration. The comparison of the experimental results with the calculated ones leads us to conclude that (1) molecularly chemisorbed species, Co(n)(+)(CH(3)OH)(m) (m=1-3), and dissociatively chemisorbed species, Co(n)(+)(CH(3)OH)(m-1)(CH(3))(OH), are dominant and (2) the methanol dehydrogenation proceeds via an intermediate, Co(n)(+)(CH(3))(OH).

Structures of nickel cluster ions adsorbed with methanol, Ni3+ (CH3OH)m (m = 1-3) and Ni4+ (CH3OH)m (m = 1-4) were investigated by using infrared photodissociation (IR-PD) spectroscopy based on a tandem-type mass spectrometer, where they were produced by passing Ni3,4+ through methanol vapor under a multiple collision condition. The IR-PD spectra were measured in the wavenumber region between 3100 and 3900 cm-1. In each IR-PD spectrum, a single peak was observed at a wavenumber lower by approximately 40 cm-1 than that of the OH stretching vibration of a free methanol molecule and was assigned to the OH stretching vibrations of the methanol molecules in Ni3,4+ (CH3OH)m. The photodissociation was analyzed by assuming that Ni3,4+ (CH3OH)m dissociate unimolecularly after the photon energy absorbed by them is statistically distributed among the accessible modes of Ni3,4+ (CH3OH)m. In comparison with the calculations performed by the density functional theory, it is concluded that (1) the oxygen atom of each methanol molecule is bound to one of the nickel atoms in Ni3,4+ (defined as molecular chemisorption), (2) the methanol molecules in Ni3,4+ (CH3OH)m do not form any hydrogen bonds, and (3) the cross section for demethanation [CH4 detachment from Nin+ (CH3OH)] is related to the electron density distribution inside the methanol molecule.