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Resonance Raman Spectra of Halogen Molecules Adsorbed on Metal Substrates

Published online by Cambridge University Press:  26 February 2011

Takeo Matsushima
Affiliation:
Chemistry Department of Resources, Faculty of Engineering, Mi'e University, Tsu 514, Japan.
Masahiro Kawasaki
Affiliation:
Chemistry Department of Resources, Faculty of Engineering, Mi'e University, Tsu 514, Japan.
Hiroyasu Sato
Affiliation:
Chemistry Department of Resources, Faculty of Engineering, Mi'e University, Tsu 514, Japan.
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Abstract

Resonance Raman spectroscopy was used to monitor the adsorption of halogen molecules (bromine and iodine) on metal substrates. The Raman bands of chemisorbed, physisorbed and crystalline species were found in the spectra. In the case of bromine, when the temperature was raised from 77 K, the band associated with the chemisorbed species increased in intensity with the concomitant decrease in intensity of the band of crystalline species. A similar increase in the band intensity of the chemisorbed species at the sacrifice of that of the crystalline species was found on continued laser irradiation. The saturation of the band intensity of chemisorbed species was found in the latter case, however. The continued evaporation of bromine vapor onto the substrate surface at 77 K with the simultaneous monitoring of the layer thickness revealed that the initial deposit of bromine onto the substrate did not lead to the chemisorbed species. The accumulation of the crystalline species occurred in its stead. The occurrence of the molecular transfer process from the crystalline species into the chemisorbed species was suggested. The Raman excitation profile showed that bromine molecules adsorbed on a substrate do not dissociate in the wavelength range studied (16000-22000 cm-1). The excitation profile is to be given by Albrecht's A term and roughly corresponds to the absorption spectrum of thin film of bromine on the substrate, which is very difficult to obtain directly.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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References

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