Characterization of alkali-metal sols in diethyl ether. Visible extinction and surface-enhanced Raman spectra

✍ Scribed by B. Bozlee; B. Lian; J. Kahn; Robin L. Garrell; Tonya Herne; A. Leiden; P. Palko; N. Hess; G. Exarhos

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 622 KB
• Volume: 196
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(92)85717-o

✦ Synopsis

Colloidal suspensions of Na, K, Rb, and Cs have been prepared in diethyl ether. The visible extinction spectra of each are compared with results of theoretical Mie-scattering spectra, calculated using a variety of optical constant data sets. Comparison of the experimental extinction spectra to the theoretical spectra demonstrates that fresh sols of Na, K and Rb contain small metal particles with diameters suitable for surface-enhanced Raman (SER) spectroscopic studies. Fresh Cs colloids, reported for the first time, show signs of particle aggregation in long strings. Raman spectra of Na, K and Rb colloids are presented in the region between 150 and 700 cm-'. We find that Na colloids display two broad SER features at 290 and 530 cm-', K colloids display two SER features at 220 and 480 cm-', and Rb colloids display one band at 2 15 cm-'. The lower-frequency bands for Na and K sols and the 2 15 cm-' band of Rb sols may be due to lattice modes of amorphous alkali-metal hydroxides on the metal surfaces. The two higher-frequency bands at 480 and 530 cm-' remain unassigned.

Alkali-metal colloids in organic media were first prepared over 60 years ago [ 1,2]. However, the physical properties of the sols have not been carefully examined. In particular, no experimental visible extinction spectra, which provide information on the particle size distribution, have been published previously for liquid suspensions. Only in the solid phase, under matrix-isolation conditions, have the extinction spectra of alkali-metal colloids been reported and analyzed carefully [ 3 1. Employing electromagnetic theory and known optical constants,