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1 May 1992 Transition saturation in ethylene observed with infrared photothermal spectrometry
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Pulsed infrared laser excited photothermal spectroscopy is used to study the nonlinear infrared absorption character of ethylene. Ethylene exhibits apparent optical saturation when high irradiance CO2 lasers are used for excitation. In these experiments a pulsed TEA-CO2 laser tuned to the 1OP(14) line at 949.49 cm-1 is used to excite the v7 transition of ethylene and photothermal lens spectrometry is used to monitor the resulting thermal perturbation. The data are obtained as the thermal lens signal versus excitation irradiance, linearized to account for nonlinearities in the apparatus response, and processed to yield 'apparent' absorption coefficient versus excitation irradiance. Apparent absorption coefficient data are then modeled based on the vibrational energy level structure and the interaction of the Gaussian excitation source with the nonlinear system. Assumptions are used to derive a reasonable vibrational state model based on probable excited states involved in the kinetic saturation. Saturation irradiance and related parameters for ethylene in Ar, He, and N2 buffer gases are given. The saturation irradiance results suggest a vibrational relaxation up to 4 orders of magnitude faster than shown in previous work. This high relaxation rate is probably due to a break down in the steady state aproximation used to solve the rate expressions.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Stephen E. Bialkowski and Zhi-fang He "Transition saturation in ethylene observed with infrared photothermal spectrometry", Proc. SPIE 1637, Environmental and Process Monitoring Technologies, (1 May 1992);

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