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Method development: time-windowing Fourier transform absorption spectroscopy for flash photolysis investigations

A technique for recording time-resolved absorption spectra using a commercial continuous-scan Fourier transform spectrometer (FTS) is presented. The method has been designed for the observation of experiments at temporal resolutions from 10(-4) to 10-2s, with delays longer than a second between two experimental repetitions. This is accomplished by synchronizing the observed experiment to certain positions of the interferometer-scanning mirror. Unlike other interleaving or stroboscopic techniques, a trigger is not generated for every interferogram point. Instead, time windows are used that are several interferogram points wide. For experiments with a low repetition rate (0.1-1Hz), the approach has advantages concerning measurement time and spectral resolution when compared to the step-scan and to fast-synchronized continuous-scan methods. The time-windowing Fourier transform spectrometer (TW-FTS) has been implemented as a hardware and software add-on to a commercial continuous-scan Michelson interferometer. No changes were made to the instrument. Two validation experiments were carried out by observing the formation and self-reaction of BrO after the flash photolysis of a Br-2/O-3 mixture at 298K. The experimental concentration-time profiles were in good agreement with decay curves from a chemical kinetics simulation of the experiments. Further, a LTV absorption spectrum of BrO, recorded by the TW-FTS method, had a comparable quality as a static FTS recording.

Citation: Fleischmann, O.C.; Orphal, J.; Burrows, J.P. Time-Windowing Fourier Transform Absorption Spectroscopy for Flash Photolysis Investigations, Journal of Photochemistry and Photobiology A: Chemistry 157, 127-136, 2003.

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Institute of Environmental Physics and Remote Sensing IUP/IFE, UNIVERSITAET BREMEN
Postfach 330440
28334 BREMEN