NEAR INFRARED MEASUREMENTS OF VOLATILE ORGANIC COMPOUNDS USING DIODE LASER CAVITY RINGDOWN SPECTROSCOPY

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2005

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Ohio State University

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Absorption cross-sections of the C-H stretching overtones of benzene, chlorobenzene, 1,2-dichlorobenzene, and toluene have been measured in the NIR (5970 to 6135 cm$^{-1}$) using CW-Cavity Ringdown Spectroscopy. The wavelength-dependent absorption cross-sections were obtained with both an external cavity diode laser and a free space DFB diode laser. Low-pressure samples (0.01 to 2.0 Torr) were introduced into an evacuated cavity. The experimental room temperature absorption cross-sections obtained for these four volatile organic compounds were found to vary in intensity from approximately are 1.2 x $10^{-22}$ to 6.9 x $10^{-21}$ cm $^{2}$, depending on the wavelength and molecular structure. The substitution of 1 or 2 Cl atoms causes a spectral shift to the blue relative to the benzene peak, whereas the substitution of a methyl group causes a red shift.

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Author Institution: Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Starkville, MS 39759; Department of Physics and Astronomy, University of Southern Mississippi, Hattiesburg, MS 39406

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