A new method for recording time-resolved absorption spectra using a commercial
continuous-scan Fourier transform spectrometer is presented. The observed
experiment is synchronized 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 of several
interferogram points are established. The new method is therefore called
"Time-Windowing Fourier Transform Spectroscopy (TWFTS)".
Based on the TWFTS technique, the UV absorption cross section spectra of the
atmosphericly important radical BrO have been determined. The
bromine-photosensitized decomposition of ozone was observed at five different
temperatures between 203 and 298 K. The spectral resolution was 3.8 cm-1.
The absorption cross section was determined from the time resolved observation
of reactant and product absorptions and by a subsequent kinetic analysis of the
experimental curves. The integrated UV absorption cross section of BrO was
observed to be
constant over the temperature range studied, as expected from spectroscopic
considerations. Based on the TWFTS spectra, vibrational constants and the
dissociation limit for the excited electronic state A2Pi3/2 of BrO were
determined. Further, the A<-X dissociation energy was estimated.
A new method for the synthesis of OBrO, using an electric discharge chain, was
established. It yielded a high concentration under flow conditions and allowed
the first observation of OBrO by a Fourier transform spectrometer. Absorption
spectra of OBrO were recorded for the visible spectral range at 298 K and a
spectral resolution of 0.8 cm-1. The high spectral resolution allowed
a vibrational and rotational analysis of the visible spectrum. New vibrational
bands were observed that could be attributed to the progression
(2,v,0)<-(1,0,0). Vibrational constants were determined for the electronic
states C(2A2) and X(2B1). For the first time, rotational constants were
determined experimentally for the upper electronic state C(2A2). By modeling the
band contours, predissociation lifetimes could be estimated. Finally, an
estimation of the absorption cross section of OBrO was derived from bromine
budget considerations.