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The region of the electromagnetic spectrum below 200 mμ has great potential for analytical and molecular structure studies. Difficult instrumental problems must be overcome in obtaining spectra below 200 mμ, but the Beckman DK spectrophotometer has been modified to perform acceptably as far as 175 mμ. Two recent reviews have appeared on the instrumentation of far ultraviolet spectroscopy [1,2]. The most recent reviews summarizing the spectral studies on organic compounds are considerably older [3,4]. All materials absorb intensely somewhere in the far ultraviolet. The spectra are often very discrete—a condition that favors analysis. Absorption occurs through electronic, vibrational, and rotational transitions of molecules so that very complex looking spectra can be obtained from simple molecules. Ionization occurs usually below 175 mμ. Almost all of the published spectra below 175 mμ have been of gases; however, solvents are available with sufficient transparency in thin cells to obtain solution spectra to 175 mμ. Water, cyclohexane and purified perfluoro hydrocarbons can be used. Of course these solvents must be pure . Of the common elements, oxygen, nitrogen, sulfur, bromine and iodine absorb in the 175 to 200 mμ region. Most of the organic and inorganic compounds containing these elements will absorb in this region. In the vapor phase, these compounds may absorb discretely. In condensed phases the absorption is usually diffuse. The atomic nature of the absorption is usually not sufficiently characteristic in shape or wavelength to identify the atom in an unknown compound.
Beckman Instruments, Inc., Fullerton, Calif.