Metal cluster ion photofragmentation

Journal of Chemical Physics - Tập 84 Số 6 - Trang 3078-3088 - 1986
P.J. Brucat1, Lan Zheng1, C. L. Pettiette1, Shihe Yang1, R. E. Smalley1
1Rice Quantum Institute and the Department of Chemistry, Rice University, Houston, Texas 77251

Tóm tắt

Photofragmentation studies are described for mass-selected transition metal cluster ions cooled in a supersonic expansion. Examples of the spectral utility of this technique are presented in the cases of Ni+2 and Nb+2 for which well resolved vibronic bands have been recorded by monitoring fragment yield as a function of dissociation laser wavelength. For larger, more complicated metal clusters the absorption spectrum is far too congested and perturbed for analysis, but photodissociation can reveal the thresholds and time scales of various fragmentation pathways. The order of the absorption event leading to dissociation is found from the extent of fragmentation as a function of laser fluence. Using this method, the one-photon dissociation threshold of Fe+2 is found to lie between 2.43 and 2.92 eV, which determines the binding energy of this transition metal dimer cation. Combined with previous ionization potential measurements this places the binding energy of the Fe2 neutral between 0.83 and 1.32 eV. Similarly, the threshold for dissociation of Fe+3 into Fe+2 +Fe was found to lie between 1.17 and 2.18 eV, placing the Fe3 neutral binding energy between 1.27 and 2.38 eV. For all transition metal clusters measured (Fex, Nix, and Nbx with x between 2 and 10) the primary one-photon fragmentation pathway was always found to be loss of a single metal atom from the cluster. Far more accurate measures of these dissociation thresholds should be possible with more extensive measurements of cold cluster ion photodissociation as a function of wavelength. Arguments are presented to the effect that these dissociation thresholds should generally provide valid measures of the true binding energies of transition metal clusters.

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Journal of Chemical Physics

Tập 84 Số 6

3078-3088

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