Ultraviolet absorption spectrum of gaseous HOCl

Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado, United States
The Journal of Physical Chemistry A (Impact Factor: 2.69). 10/1986; 90(22):5578-5584. DOI: 10.1021/j100280a021


The UV absorption spectrum of gaseous HOCl was investigated in the wavelength region 240 to 390 nm by using a dynamic HOCl source. Substantial quantities of HOCl were produced compared to two species (Cl2O, ClO2) that are spectral interferences in the wavelength region of interest. Thirteen experimental absorption spectra were analyzed by the statistical method of factor analysis. This analysis revealed that two major components were contributing to the total absorbance in each spectrum and that these two components accounted for 99.97% of all variance in the data. Mass spectra were simultaneously recorded with the absorption spectra by a quadrupole mass spectrometer that was calibrated for HOCl, Cl2, Cl2O, ClO2, and other species. The two components in the absorption spectra were identified as Cl2 and HOCl containing trace levels of ClO2. The isolated Cl2 and HOCl/ClO2 spectral curves were obtained from a spectral isolation factor analysis and quantified by using the Cl2 spectrum as an internal standard. Atmospheric photolysis constants averaged over 24 h were calculated as a function of altitude form the cross sections generated in this work predict a shorter photolysis lifetime for HOCl above 28 km. This results in a 6 to 19% decrease in the predicted HOCl diurnal average concentration in the altitude region 28 to 34 km, respectively, compared to the concentrations predicted by the currently recommended cross sections.

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