The interaction of gold clusters with methanol molecules: Infrared photodissociation of mass-selected Au-n(+)(CH3OH)(m)

Structural and energetic properties of the adducts formed by adsorbing meth anol onto size-selected gold clusters are investigated by infrared photodis sociation of trapped Au-n(+)(CH3OH)(m), n=1-10,15 and m=1-3. The excitation of vibrational modes of methanol leads to the desorption of neutral molecu les which is monitored by time-of-flight mass spectrometry. Spectra are obt ained by measuring the fragment ion intensity as a function of photon energ y. The C-O stretching vibration of adsorbed methanol changes discontinuousl y with cluster size. By comparison with Car-Parrinello calculations this ch ange is traced back to the dimensionality of the gold clusters. The number of photons necessary for the desorption of methanol molecules provides an e stimate of the respective separation energies. (C) 2000 American Institute of Physics. [S0021-9606(00)01302-7].