New measurements of OClO absorption cross-sections in the 325–435 nm region and their temperature dependence between 213 and 293 K

Absorption spectra of gas-phase OClO in the 325–435 nm region (23,000–31,000 cm−1) have been measured at five atmospheric temperatures between 213 and 293 K with a spectral resolution of 1.0 cm−1 using Fourier-transform spectroscopy. Absolute absorption cross-sections of OClO at 293 K have been determined and were also used to scale the spectra at the lower temperatures to absolute cross-sections. The results are in good agreement with previous studies of the OClO cross-sections but provide a better coverage of atmospheric temperatures. In addition, Fourier-transform spectroscopy has the advantages of an accurate wavelength calibration and of high spectral resolution. The new cross-sections are important as reference data for remote-sensing of OClO using UV-Vis absorption spectra of the Earth’s atmosphere from ground and space. The new spectra were also used to fit the OClO Ã−X̃ electronic band centres in order to re-determine the upper state’s molecular constants. In a second set of experiments we investigated the photolysis of pure OClO leading to the formation of Cl2 and higher chlorine oxides as further products. To provide a qualitative understanding of the photolysis mechanism a chemical reaction simulation was carried out using the FACSIMILE© software.