16) Fales, H. M.; Lukkainen, T. Anal. Chem. 1965, 37, 955. (17) Burgett, C. A.; Smlth, 01. H.; Bente, H. B.

A system for the calibration of the absolute spectral response of spectrometers is described using a standard reflector -of the type used especially for colour measurements -as a secondary light source. In contrast to conventional light sources for calibrations, the radiance is approximately constant over the whole area of the source, and the angular characteristic is known for a large range of reflection angles p. A special advantage is that the angular characteristic follows closely the Lambert-cosine-law in the region q-45". The radiant flux can be calculated exactly for various experimental conditions, especially for Raman spectroscopy.

A Raman polychromator system is described which makes use of a concave grating, two objectives with f-numbers lower than 1, and a multichannel detector. The system provides a very large optical throughput and should be suitable for analysis of gaseous and liquid samples -especially in cases where the concentration of the compounds investigated is rapidly varying. This is demonstrated by measurements at automobile exhaust gases and by an on -line detection of high -pressure liquid chromatography (HPLC)-fractions. Keywords: Raman spectroscopy; linear Raman spectroscopy; multichannel spectrometer; automobile exhaust gases; on -line high-pressure liquid chromatography (HPLC) /Raman. Optical Engineering 22(3), 308 -313 (May /June 1983). Keywords: Raman spectroscopy; linear Raman spectroscopy; multichannel spectrometer; automobile exhaust gases; on-line high-pressure liquid chromatography (HPLQ/Raman. Optical Engineering 22 (3), 308-313 (May/June 1983).

The theory of the Raman intensity of crystal powders given by Schrader and Bergmann[8] describes the radiation balance of a turbid medium by a scattering module r , an absorptionmodule u and a Raman scattering module s. On the base of this theory the necessary experimental conditions and the evaluation procedure for the determination of absolute Raman scattering cross sections are given.

An investigation has been carried out on the correlation between intermolecular interactions and absoluteRaman intensities of lattice modes. The analysis was performed by comparing absolute Raman intensities (measured using crystalline powders) with those calculated according to the oriented-gas approximation. For the five organic compounds investigated, it could be shown that, in geoerd, the oriented-gas model is inadequate for the description of the properties of molecular crystals. Large discrepancies in the model could be revealed for modes with both librational and translational character. The discrepancies depend strongly on the strength of the intermolecular interactions.

A Raman multichannel system is described which is feasible for the on-line identification of fractions separated by gas chromatographic columns. In Raman multichannel systems, the sensor, i.e., the laser focus, is small enough and the possible recording times are short enough to avoid any affliction of the separation process, even with capillary columns in use. At the measurements described, capillary columns with a length of 15 m and an inner diameter of 0.25 mm were employed. The detection limit was at about 1 to 10 nl of one fraction corresponding to about 1 to 10% of the total amount of sample suited for capillary columns.

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