The sulfur compounds show a wide variety of absorption bands and an extremely wide range of absorbances. Sulfur hexafluoride has the strongest band in the database, while hydrogen sulfide is the weakest absorber in the database.

     Hydrogen sulfide might have been classified as a hydride and included in Chapter E; but in fact, the sulfur is the main determiner of properties, so the molecule is shown here instead. Since the infrared spectrum of H2S is extremely weak, its minimum detection limit that is far higher than that of other compounds in the database. Methyl mercaptan is also a weak absorber, but not as weak as H2S. The way to measure both of these compounds with high sensitivity is to use by PAPA technique developed by Infrared Analysis, Inc. PAPA is the acronym for photolysis assisted pollution analysis in which sulfur compounds are converted to other molecules, such as SO2, which are more easily measured. Refer to the article on PAPA.

     Sulfur dioxide is the most important member of the group. In atmospheric studies the strongest SO2 band at 1360 cm-1 overlaps with water absorption. At very long paths in air the 1150 cm-1 band is the one most likely to be seen. If the atmospheric path is kept down to no more than 100 meters and if water absorption is properly subtracted from the spectrum, the 1360 band can be seen and measured with PPB sensitivity.

     Sulfur hexafluoride is a commonly-used tracer compound in atmospheric studies. The compound can be measured easily by its infrared absorption using the extremely strong band in the clear region near 950 cm-1. See SPECTRA, chapter O.

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