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.
[Show abstract][Hide abstract] ABSTRACT: The theoretical photoabsorption cross sections of HOCl and HOF are obtained with ab initio MO CI calculations. The theoretical spectrum of HOCl shows two peaks at 180 and 258 nm, and the spectrum both in shape and in intensity was in agreement with the experimental one. It is concluded that HOCl does not play a significant role as an inert chlorine reservoir in the stratosphere. The theoretical absolute absorption cross section of HOF is also in agreement with the experimental one below 200 nm.
Chemical Physics 07/1989; 135(1):75–83. DOI:10.1016/0301-0104(89)87006-5 · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nascent OH rotational distribution has been observed following the 248 nm photolysis of HOCl in a supersonic molecular beam. A strong preference for the population of the OH 2Π3/2 spin state is found and a significant deviation from the statistical population of the OH lambda-doublet states is observed. The OH rotational distribution can be characterised by a temperature which is slightly different for the two spin–orbit states. These rotational temperatures decreases as the pressure of the Ar carrier gas used in the supersonic expansion is increased, but the spin–orbit population ratios and the lambda-doublet preference is essentially the same under all the expansion conditions studied. The experimental observations are consistent with dissociation from a 1A′ excited state and the rotational energy of the OH fragment originating partially from the zero-point bending motion of the HOCl and partially from the parent rotational motion.
Journal of the Chemical Society Faraday Transactions 12/1990; 86(23). DOI:10.1039/ft9908603831 · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Potential energy surfaces for electronic ground and excited states of HOCl, which are related to the experimentally observed photoabsorption between 400 and 200 nm, were calculated with the ab initio molecular orbital (MO) configuration interaction (CI) method. The transition dipole moment surfaces between these states were also calculated. Two types of model calculations were carried out for evaluation of the theoretical photodissociation cross section. Theoretical spectra exhibit two peaks at about 335 and 245 nm. They are in better agreement with the experimental results than those in the previous study (Nambu, S.; et al. Chem. Phys. 1989, 135, 75). The present calculation supports the assumption that the HOCl molecule in the stratosphere may contribute to ozone depletion. The rotational state distributions of the product OH(2-PI) were explored with classical trajectory calculations. The rotational state distributions are dependent on the excited state.
The Journal of Physical Chemistry 03/1992; 96(5). DOI:10.1021/j100184a017 · 2.78 Impact Factor
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