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 10−2 s, 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 (0.1–1 Hz), 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 Br2/O3 mixture at 298 K. The experimental concentration–time profiles were in good agreement with decay curves from a chemical kinetics simulation of the experiments. Further, a UV absorption spectrum of BrO, recorded by the TW-FTS method, had a comparable quality as a static FTS recording.