A new instrumentation technique used by Edgar S. Etz and Gregory S. Rosasco at the National Bureau of Standards successfully identified the particulates emitted by oil-fired power plants. Such detailed molecular identification is needed to assess the effect of pollutants on people and the environment. Since previous data on the chemical properties of fly ash are largely limited to the elemental composition of bulk samples of particulates collected in the stack and in the plume of power plants, the NBS molecular identifications are of great interest.
The NBS unique laser-Raman microprobe is designed for spectroscopic analysis of microparticles. Single particles, supported by a suitable substrate, are moved into the focal point of a laser beam (utilizing any one of several ‘excitation’ frequencies in the visible region of the spectrum), and the light scattered by the sample is analyzed for its spectral content. The scattered light contains the Raman spectrum of the particle which is diagnostic of molecular and crystal vibrations in the solid. Particles composed of a broad range of inorganic compounds, organic solids, and polymers show the normal Raman effect and can therefore be identified as to principal molecular constituents.