Detection of OH Stretching Mode of CH3OH Chemisorbed on Ni3and Ni4by Infrared Photodissociation Spectroscopy.

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 Ni3,4through 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 ∼40 cm-1than 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)mdissociate 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)mdo not form any hydrogen bonds, and (3) the cross section for demethanation CH4detachment from Nin(CH3OH) is related to the electron density distribution inside the methanol molecule. [ABSTRACT FROM AUTHOR]