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Liquid filters for Raman Resonance Raman provides an added degree of selectivity over normal Raman spectroscopy, but the rejection filter requirements can be far more stringent for resonance Raman because many organic compounds strongly absorb only in the UV. For example, a 500-cm"1 Raman shift is 14 nm from the 514.5-nm argon ion laser line but only 3.6 nm from the 266-nm line eo a quadruple Nd:YAG laser. Therefore, a sharp spectral cutoff is crucial for any filter that will be used for Rayleigh rejection in UV-resonance Raman spectroscopy. Joel M. Harris and colleagues at the University of Utah constructed Rayleigh rejection filters with easily prepared solutions of inexpensive and readily available organic compounds. The filters were insensitive to polarization and could be placed anywhere within the collection optics of the Raman system. Solutions of 1,2-dichlorobenzene in heptane, 1,2,4trichlorobenzene in heptane, potassium hydrogen phthalate in water, hydroquinone in ethanol, and 2-naphthol in hexanol were used as rejection filters for UVRaman spectroscopy of CC1 at the 288- 299- 309- 316- and 342-nm linee respectively of a Raman-shifted Nd'YAG laser Raman scattering could be observed within 200 cm"1 of the Rayleigh line The Rayleigh rejection efficiency which was on the order of 102-103 could be improved by increasing the chromoohore concentration but only at the exDense of Raman scattering throughput (AM Stectm
