Abstract

Raman spectroscopy is applied to the physical and chemical characterization of an electrostatically charged single microparticle, which is trapped and suspended in an electrodynamic cell. The microparticle, 10 to 15 pm in diameter and composed of deliquescent salts, such as sulfates and nitrates, is present either as a solid particle or as a solution droplet under controlled humidity conditions. While the chemical composition of the microparticle is characterized by the distinct Raman shifts observed, the physical state is revealed by the Raman bandwidths. Since a solid microparticle under laser illumination is largely free from both the sample inhomogeneity and optical transmission degradation that are normally encountered in a single crystal or crystalline powders, it follows that single particle suspension is a unique experimental method for measuring relative Raman scattering cross-sections for solid compounds. Furthermore, a suspended solution droplet, which evaporates to attain high supersaturations inaccessible with bulk samples, provides an ideal condition for a spectroscopic investigation of solute-solute interactions in concentrated electrolyte solutions. Experimental results are presented, which illustrate the uniqueness and versatility of single particle Raman spectroscopy.

© 1992 Optical Society of America