Search

The infrared photodissociation spectra of Fen(CH3OH)m, Fen(CH3OD)m, Fen(CD3OH)m, and Fen(CD3OD)m (n=5–15; m=1,2) have been recorded from 920–1090 cm-1. Analysis of the spectral features indicates that in all cases, molecularly adsorbed methanol is the absorbing chromophore, with no evidence of methoxy formation. The observed frequencies for the C–O stretching vibration and other vibrational modes are shifted ∼40 cm-1 to the red of the corresponding fundamentals of gas-phase methanol. The spectral shifts and thus the magnitude of the cluster–methanol interaction are observed to be independent of iron cluster size over the size range studied, implying an insensitivity of the interaction to the underlying cluster structure. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The photodissociation spectra of the copper trimer and its argon and krypton adducts have been recorded in the visible. For Cu3, we observe a number of resolved vibronic transitions to the blue of the A←X origin at 539.8 nm in accord with the observations of Morse et al. [J. Chem. Phys. 79, 5316 (1983)]. By contrast, the spectra of Cu3Ar and Cu3Kr consist of continuous absorption bands with maxima at 516 and 517 nm, respectively. While the oscillator strengths of the Cu3Ar and Cu3Kr absorption bands are nearly an order of magnitude larger than that derived for Cu3 from its photodissociation spectrum, they are in much closer agreement with the oscillator strength determined from the Cu3 A→X radiative lifetime. [ABSTRACT FROM AUTHOR]

The optical absorption spectra of niobium clusters containing 7 to 20 atoms have been measured from 336 to 634 nm by way of photodissociation action spectroscopy of the corresponding van der Waals complexes with argon atoms: Nbn Arm → hν Nbn + m Ar. The clusters in this size range do not display discrete absorption bands characteristic of molecular behavior, but rather absorption cross sections which increase monotonically with decreasing wavelength. This behavior is in qualitative accord with the absorption behavior predicted by the spherical Mie model for small niobium spheres, however, the measured cross sections are 2–5 times larger than predicted over this wavelength range, with the smallest clusters displaying the largest deviations. Interpreted within the classical electrodynamic framework, these observations suggest that the absorption spectra derive oscillator strength from an incipient surface plasmon, redshifted from its predicted resonance frequency in the vacuum ultraviolet. [ABSTRACT FROM AUTHOR]

The photoionization efficiency spectra of nickel clusters containing adsorbed ammonia have been recorded near threshold. Ionization potentials (IPs) have been assigned for 97 selected Nin(NH3)m species, with n up to 56 atoms. We observe that nickel cluster IPs decrease upon ammonia adsorption, with the magnitude of the IP shifts varying linearly with the number of adsorbed molecules, in good agreement with a simple electrostatic model. Deviations from this behavior are observed for Ni5(NH3)m and Ni6(NH3)m clusters, in which adsorption of the first ammonia molecule produces a significantly larger IP drop than do subsequently adsorbed molecules. Such behavior may indicate the presence of unique adsorption sites on Ni5 and Ni6 preferentially occupied by the first ammonia molecule adsorbed onto these clusters, or alternatively, may indicate cluster rearrangement occurring as the result of chemisorption. Our results are discussed in light of studies of ammonia adsorption onto single crystal nickel surfaces. [ABSTRACT FROM AUTHOR]

Studies the reaction of silver clusters with ethylene and ethylene oxide using the infrared photodissociation and photoionization spectroscopy. Ionization potential bracketing; Infrared photodissociation spectra; Role of silver particles in catalyzing the epoxidation of ethylene to ethylene oxide.

Transition-metal clusters are large heavy molecules possessing many low-lying electronic states, and can be produced under isolated conditions (i.e. in molecular or ion beams) only at very low number densities. As a result, many of the traditional methods of molecular spectroscopy cannot be used to study these species. However, newer techniques, developed within the last 15 years, have proven successful in probing neutral and charged transition-metal clusters. In this (selective) review, the strengths and weaknesses of these techniques are discussed, with recent examples provided. [ABSTRACT FROM AUTHOR]